JML

In case anyone needs any, here are two good sources. The first is a US source for many different types of screws.

Fastener Express: https://www.fastener-express.com/

The second is in the UK, and started as a place for motorcycle fittings, but they have a US website. Some really cool stuff, and some full kits for bicycle component groups.

Pro-Bolt: https://www.probolt-usa.com/

unworthy1

many thanks, these have been added to my bookmarks list.

cuda2k

Here's another for just about any sort of fitting, bolt, screw, nut, washer, etc etc etc you'll ever need:

https://www.mcmaster.com/

OTS 

Here's yet another

https://www.boltdepot.com/

LesterOfPuppets

My local True Value Hardware carries most metric bolt sizes needed on a bike.

Those are good links for when I retire and start yard sale bike wrenching full time, however.

JML

Amen to that! I have many, many parts and items bookmarked on McMaster's site, but for other hobbies. Their prices are fairly high for small amounts of things, given that they're an industrial supply house, but they're literally a one-stop shopping site for hardware, tools, etc.

Mike Mills

I needed some wierd screw for my bike. It was about $15-$20 by the time I got my hands on it. It was a 5/16 X 3/4" with 28 tpi in stainless steel in a socket thead configuration. Whatever it was, it was almost impossinble to find.

mudboy

I always use McMaster-Carr. I have a feeling that if they ever let me into their warehouse, they'd never get me out.

EAA

I have had consistently excellent experiences with McMaster-Carr. For the stuff I've bought (more fasteners than anything else) their prices usually are competitive for same quality/brand, shipping charges very reasonable, service great. With standard ground shipping I usually receive my order in less than 24 hours - I'm not too far from their headquarters in Illinois, but still think that's pretty impressive.