You can't get them super cheap, unless you're really lucky. I get stuff from ebay (it involves a lot of stalking listings, and knowing when to give up - they can get very expensive). I haven't actually bought any in months and months so i couldn't tell you if it's still that competitive but i would guess so. What ever you do though DON'T buy them from etsy, it's such a rip off!
If you can get big listings of stuff then that's always best - listings with like 20-50 pocketwatches will get very expensive, but i rationalize it by how much i'm paying for each one.
(I'm actually thinking of selling some of my parts as i've lost my inspiration somewhere....maybe behind the wardrobe....)