i believe they're a 5/16-18 (5/16 coarse thread), but i will admit i don't have one here to check. pull out your bin of spare bolts and see what screws in. i know they're not metric. as for length, i would have to suggest using a tape measure, possibly with a probe (to determine hole depth). grade 5 bolts are correct for this (and most) applications, and can be found at your local hardware store. buying them from the parts store costs at least twice as much.
as for your sway bar mounting bolts, again, any bolt of proper thread size and length will do. since i'm not sure what year your car is, i'm not sure if they're US or metric, but i think its safe to say that if other fasteners on your body are metric, there's a good chance those are too. again, a US grade 5 or better (metric grade 8.8 or better) is correct.