nissan stanza and sentra similar on 1990 Nissan Stanza

i was told that you could get used parts off of sentras because stanza's are so hard to find? true or not and if so,what years?

That will depend very much on the parts involved. It may well be true, but the best thing to do is to get part numbers and your car's VIN. Then, most salvage yards or auto parts stores can help make sure you won't have a fitment issue. The years and whether it will work at all will vary by the part number.