Used Stuff
Retail Surplus
https://www.overstock.com/Electronics/2/store.html
Government Surplus
https://www.govdeals.com/ – Ohio State sells their surplus here.
Watch Parts and Tools
https://www.esslinger.com/ – has lots of tools.
https://www.startimesupply.com/ – good for batteries and miscellaneous watch parts, must be a verified business to order
http://www.julesborel.com/ – see the JBC watch parts database
Cas-Ker Watchmaker and Jeweler Supplies
– based in Cincinnati, tools and parts.
Otto Frei Jewelry Supply and Watch Parts – large selection of watch crystals
Auctions
https://www.bidfta.com/bidderHome
Miscellaneous
Mobilinkd, Terminal Node Controllers for Amateur Radio