What budget do you have?
Does it need to be a sport?
There are a few around but quite a few lemons also. Rust in the boot pockets, sunroof, arches, under windscreen are very common rust places.
If you found a clean 320, a 325 conversion is pretty easy if you have a donor car. More or less identical blocks. Could keep it as a 320 on the books as there is no visible difference.
(E30's were stopped in 1991 - except for the tourings that went on till 1993.)