As a (primarily) iOS developer by trade, I feel your pain. There are colocation operations that seem to do well. They involve racks and racks of Mac minis hanging out in a datacenter somewhere -- since it's Apple hardware, it's totally acceptable within OS X licensing terms. It costs more, of course, but it might be a valuable investment to an operation that relies on a volume of machines to be available and shareable while staving off concerns about wear and tear.

The standard, and original, is: https://macminicolo.net

I'm sure there are others.