The factory bolts do not allow for any pushing or pulling, hence the GM crash bolts...which allow exactly what you are talking about^. If you're alignment guy didn't change the bolts, all he can adjust is toe with the tie rods. At that height you are probably producing positive dynamic camber.
I would just order some online...I think I paid $13ish shipped from gmpartsdirect. You're going to have a hard time finding a bolt with adequate flange to make good contact at the hardware store. These things have a propensity to slip under hard cornering or large bumps...which is why they made it not adjustable from the factory.
I can measure them tomorrow if you really want, but its cold and I don't want to go outside. The nuts are the same as the stock size, as are the bolts except they are threaded all the way instead of a a collar on the end.