The gyros for the Dawnguard quest

According to: uesp.net

Sorine Jurard will turn up in the wilderness near an unmarked Dwemer convector, just south of Mor Khazgur. She will be drifting around, obviously looking for something, mumbling: "What would mudcrabs want with my satchel, anyway?" and "Just one gyro. One, and I can get back to work. Where are they?"

When you talk to her, she will ask if you have seen a sack full of Dwemer gyros and will proceed to tell you that a mudcrab may have taken it. When you tell her that Isran needs her help, she will respond: "Isran? Wants me? No, you must be mistaken. He made it exceedingly clear the last time we spoke that he had no interest in my help. I find it hard to believe he's changed his mind. He said some very hurtful things to me before I left."

When told about the vampire threat and the Elder Scroll, she will change her mind, although she will not do anything before she gets a Dwemer gyro. You can now choose between two options, although the second option will differ if you already have a Dwemer gyro in your inventory. If you do, you can hand it to her and she will be on her way to Fort Dawnguard.

You can also choose to persuade her, although you need a Speech skill of 50+ to be successful. If everything else fails, you can look around for her satchel, which can be found on the shore a few feet south of where Sorine stands.

When you return to her with one of the gyros she will finally be convinced and walk all the way to Fort Dawnguard for an encounter with Isran.

Dwemer (Dwarven) ruins are always a good place to go, if you can't find what the mudcrabs have 'taken'