I am used to metric as well, being from mainland Europe. But getting some 5/16-18 bolts actually wasn't that hard. A couple of years ago I bought myself a small collection of empirical-sized nuts and bolts (mainly 1/4-20 to go with my Incra T-tracks) to use in tools and jigs. Another option could be to tap a new thread with metric diameter and speed. That shouldn't be too hard, but I don't know if you have access to the required tools for that. To me buying a set of appropriate nuts and bolt has been a real time-saver (no need to adapt metal to metric sizes).