Name of part - Rear wheel spacer screw I have a single speed bicycle which has a spacer screw that controls the position of the rear wheel and hence the tension of the chain.

The screw goes through a small hole in the frame, which is threaded, and in to the drop out area. With the pair of screws at a level pegging, the proper position the wheel is assured and the chain tension is maintained.

What is the name of this part? I've bent one of my screws and need a replacement but can't find a hit on "rear wheel spacer screw."
Dropout adjustment screw.  Here's a thread from the Bikeforums with some links and such to check:

http://www.bikeforums.net/archive/index.php/t-274077.html

Unfortunately they do not appear to be standard... You might try haunting more established shops to look through their old-parts boxes.
Most hardware stores carry a very wide variety of metric fasteners; you might be able to find a suitable screw there