So are your towers rusted out... The side of the strut towers can rust on the side, but never seen the tops rust out. Just want to make sure you are not talking about the insulator, which is a black, round thing, with the 3 threaded studs that go into the holes in the tower, has a large bolt in the middle which attaches to the strut insert...
If the towers needs to be replaced, that is a major welding job! You will need the tramming info in the service manual to make sure everything is line up correctly.
I would go to a junk yard or look for a cheap parts car and cut them out. I haven't seen anyone selling pre-fabbed ones yet. You can always make it into a tube chassis then add aluminum paneling for the inner fenders.
If looking stock is of concern then I would look for a donor car.