Thermostat housing bolts size on 1990 pontiac sunbird?

busted 2 of the bolts, really rusty, got it soaking with liquid wrench.....anyhow im gonna need to go and get 2 more bolts when i get the others out. I need to know if anyone knows the EXACT size and where to get them? i can prob get them anywhere but i want the exact ones...hardness is prob the difference.