I have a toyota mainshaft out of the t case that I did some work on and would like to reheat treat it any company recommendations are appreciated that will do small orders:D :D

go to a local machine shop and ask them who they use to heat treat

The first question a heat treater would (or should) ask is what material is it? Most heat treaters probably won't touch it unless they know what material it is. The trick is going to be finding that out, good luck. You usually pay by the pound, but there is a minimum, at least $150.