Ametric is a nifty fastener-supply place on Clybourn that I just discovered that looks like a great place to get fasteners. I serendipidously found them through a not-particularly-intelligent Google search - I had been trying to track down a socket-head cap screw of just the right length that I needed to install a new set of brakes with my front rack. It is run by a 60-something-looking French couple. I called them on the phone, she said 'sure, we've got that.' Came over after work with my reference bolt in hand and got what I needed in a minute. They've probably got whatever you might like in stainless, which in my experience is rather hard to find. A lot of people don't care about fastener material or finish, but eventually my attention-to-detail gene takes over and my non-SS fasteners eventually look ugly. 

They are at 2461 N. Clybourn - they are extremely easy to miss, as the only signage is a paper sign on the door - easier to look for the number. They're on the east side after Fullerton and before the railroad underpass.