Suite101 has a well written guide on the location of the Seven Sages.
The only sign you get of Ghetsis is a message from his Shadow Triad that he's disappeared for the time being as you try to cross the Marvelous Bridge, east of Nimbasa City. They'll give you the Adamant, Lustrous and Griseous Orbs, all formerly held by the main legendary Pokémon of Diamond, Pearl and Platinum, before disappearing. Consequently, you can't actually catch Ghetsis.
First up, then, is Sage Zinzolin. Remember when you fought off Team Plasma in the Cold Storage area in Driftveil City? Zinzolin is there, way back in the same freezer where you found the whole team huddled in a mass. He gives you TM01, Hone Claws.
Second is Sage Bronius. He's probably the most annoying of the sages to find, as he's hiding in the depths of the Chargestone Cave, an area you have no real reason to revisit otherwise. Look in the southern reaches of the bottom level of the cave. Be ready, as he's protected by two Team Plasma grunts. You'll get TM69, Rock Polish, from him.
Third is Sage Rood. He's in an isolated spot way at the western edge of Route 18, just off Route 1 at the beginning of the game. He'll give you TM32, Double Team.
Fourth is Sage Ryoku. Descend into the Relic Castle again and you'll discover a new set of passages you can enter. Inside you'll find a maze, and after getting through the maze (which isn't terribly difficult) you'll find Ryoku. He'll give you TM04, Calm Mind.
Fifth is Sage Gorm. Go back to the Dreamyard east of Striaton City, enter the basement, fight off the trainers there if you haven't already and make your way to the second ruined building at the other end of the passages. You'll find Gorm waiting, and he'll give you TM75, Swords Dance.
Sixth and last is Sage Giallo, the only sage in the post-game sections of Unova. Teach Waterfall to one of your Pokémon and ascend the falls scattered around Route 14 to find him. Giallo gives you TM08, Bulk Up, before Looker thanks you one last time and carts the villain away.
According to Bulbapedia, there are 4 Pokemon with the ability Wonder Skin.
Sigilyph's Slot 1 ability is Wonder Skin, so you do not need Dream World access for this.
However, with Venomoth, Skitty, and Delcatty, for whom Wonder Skin is a hidden ability, this is more difficult.
In Pokemon Black 2/White 2, there are only a few sources of Pokemon with hidden abilities that do not involve connectivity to the 3DS (Dream Radar), or the Nintendo servers (Wi-Fi/Global Link Event, Dream World).
For future reference, in case another Dream World ability catches your eye, you can obtain these Pokemon through:
Venonat can be found in the Hidden Grotto on Route 3 (Pond). Evolving Venonat will give you a Venomoth with Wonder Skin.
However, neither Skitty nor Delcatty can be found in Hidden Grottoes, nor do the in-game events contain their Dream World variants (Such events include the recurring Braviary on Route 4, and Musharna in the Dreamyard). N's Pokemon can only be caught if you performed a memory link with a previous game (difficult to do without using the physical White 2), but it appears that N did not have Skitty nor Delcatty.
The last legal/legitimate option in this case would be to breed a fresh Skitty. However, since the Pokemon cannot be obtained any other ways, this is a bit of a Catch 22. But if you would like some peace of mind about using "Genetically Modified Pokemon", you can utilize save editing software to give yourself a temporary female Dream World variant to breed, and then release it afterwards, keeping the eggs. Because most Dream World Pokemon arrive in the Entralink at Lv 10, hatching a Pokemon at a low level would probably feel more legitimate.
Save restoration through the link given above by Theodore is also a good idea. I would suggest that perhaps you enable Memory Link on your physical copy after dumping your save file onto it, to allow for N's Pokemon to be caught when you play on your emulator again.
Finally, a full list of Dream World variants and their in-game locations can be found here.
Best Answer
DeSmuME does not officially support the main series Pokemon Games:
While not the nicest way of putting it, it's a fair assessment. Emulators like DeSmuME are only 'pretending' to be the original DS hardware, and they may not support 100% of the games nor all the features of the DS.
It's also worth mentioning that the latest stable version of DeSmuME (as of writing) is 0.9.11 - it's still being actively worked on, and is not considered a finished product. There may still be bugs hidden away in the emulation code that are not immediately apparent but cause issues/glitches with games.
As an example - the emulator may not fully emulate the game's clock correctly, introducing errors into time-based events like the ones your seeing. Pokemon games are notorious for shutting down time events for 48 hours when they detect a change to the system clock (even for perfectly legitimate reasons like Daylight Savings changes). This functionality is built to prevent people cheating by changing the clock to speed up processes like berries growing, or trainers requesting rematches.
So what can you do?
To avoid most time-breaking issues, I would recommend not using Save states - only Save and Load using the in-game 'Save' function. Also avoid any 'fast-forward' features (if any). This should at least limit the impact of time glitches on your save game.
If the issues are still occurring after that, then you may have to look into other options such as purchasing a DS to play on (relatively cheap now in most second-hand electronics stores!), or finding another emulator that supports the Pokemon games better.