Pretty much everyone is switching over to TU-2s probably for the same exact reasons that you want one. So I doubt you are going to find anyone willing to give one up for a conventional tuner. Just my opinion, but I think you'd be better off just selling the TU-12 for whatever you can get and putting that money towards just buying a TU-2, used or otherwise.
just get a A/B box and use the TU-12 as a silent tuner and keep it out of your signalchain when not in use.....don't think the TU-2 has anything more to offer as a tuner..in fact the TU-2 has been reported as a bigtime tonesucker by people on theis forum... i have my TU-12 nearly 20 years and it's still on my board and on the boards of a lot of bigtime pro's....