My preferred bits source:
http://www.thewarstore.com/cgi-thewarstore/sb/productsearch.cgi Mostly aimed at
SM, but I can see some conversion happening there. (Also search "Steampunk" for bits as well)
Ebay is another great source:
http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=28mm+mechanical+wings&_sacat=0 If you've got anything with wings, this will work wonders on "Mechanical."
http://stores.ebay.com/Kromlech-Bits-and-Minis?_rdc=1 Not sure about scale. Looks mostly for orcs, but again, depending on scale there could be many possibilities
I just found this wonderful looking bit source:
http://www.shapeways.com/ 3D printing. Want 20 custom Should-pads? Just bookmarked a few pages myself for my Carcharadons Astra. I saw mechanical bits but they looked a tad crappy. Search around and see what you can get. Also unsure about scale and fit, and quality. Buy something cheap first, then go from there I guess
http://www.zealotminiatures.co.uk/#!__zealot-store/robotic-arms Robotic Arms anyone?
NECRONS! Get necron bits, and daemon them up a bit. I've never worked with them myself, but you're a daemon player, you can think of something interesting
My only other guess would to keep working on your Google skills
Search terms like:
"28mm + bionic bits"
"28mm + mechanical bits"
"28mm + sci fi conversion bits"
etc.
Good luck