I'm guessing that this is more of a curious question than someone who actually wants to buy a wombat but I doubt you could get one, I think it's illegal to keep them plus he'd have a pretty strong but, their backsides are very hard and they are strong enough to crush bone, personally that would scare me
The crown has banned all export of marsupials from down under. This would include wombats in the ban. There are no US breeders. The only Wombat Farm I found now breeds only alpacas.