the-elder-scrolls-v-skyrim
I would like to buy lots and lots of Soul Gems. Petties etc.
It's to train Enchanting.
I can't find a reliable source that constantly has a good supply.
(Aside from Collette at the Mages College, and the Wizard in Dragons Reach, I can't find anyone else?)
In order to charge a soul gem, you need to use the Soul Trap spell: merely killing enemies isn't enough. Cast Soul Trap, then kill the enemy, and the gem will get charged.
If you have a weapon with the Soul Trap enchantment, that'll work as well.
The Cronvangr Cave in Eastmarch is full of weak spiders, I usually hunt there.
Map, courtesy of the Elder Scrolls Wikia:
Best Answer
I'm surprised nobody else has said it yet but, BLACKREACH!
There are a million dwarven machines that drop them, the falmer carry them sometimes, and finally, and the best part, you can mine them. Bring your pickaxe. Look for "Geode Veins." I haven't seen it mentioned anywhere else but a geode vein is where soul gems come from. You mine it like just like iron or ebony ore.
I suggest using a weapon enchanted with soul trap also because every falmer you kill will go right into filling an empty gem. When I got done I had about 60 or so filled soul gems and leveled from enchanting 50 to 100 with the one trip!
Do the quest to find 30 crimson ninroots while you're at it and you'll run into all the geode veins.