Your chances of finding anything „off the shelf“ are slim, but I wish you luck!
Have you considered using hard-cast bullets? Getting a mould made to your specification would not be a problem. But buying jacketed bullets made to order will be a bank-breaker, as you would effectively have to order a lifetime‘s supply in one lot to bring down the unit cost and to ensure that you still have supplies in a couple of years time.
BTW, I once met a guy who uses home-made bullets for his BMG50 - also an expensive taste in ammo! He reforms cartridge cases (45-70, I seem to recall) and fills them with lead to create a bullet with a nearly-complete jacket but with a bare lead nose. If you have the time, that seems like an interesting possibility.
However you load it, if you do acquire a T-Gewehr, please tell us all about it!
Patrick