RE: Decisions, decisions....
Reindeer - If you are even considering the 1:9 Abrams I think that you should also keep the Hen Longs in mind. Do like Tom said and try to find people in your area that have some tanks.
The only thing about the modern armor HL's is that like the VS tanks they are only 1:24 which might not suit your desires. Replacement parts are the only things I have found for the 1:24 HL's and they are only tracks and gearboxes. There might be parts out there for them but I haven't really needed to search for them, so I can't help you there. If you didn't mind the WWI era tanks I'd be more than happy to help as I am in the process of modifying and upgrading my HL Tiger as we speak.
With your criteria I would more than likely buy the VS tanks. You can talk to your LHS (if you have one) and try to order them locally, which might help you out with the online buying problems you noted. You can still detail it any way you want, and it will give you some ideas on how to scratch build one later on if you still desire to do so.