Just go to a decent radiator shop, or discount parts store like Kragen or Grand auto, and order a replacement radiator for a '93 - don't need a part #... My replacement ran about $180, misc hardware and new upper hose put me right at $200 - only large extra item might be a new thermostat housing that has the right angle on it for the crossover hose - I simply cut mine with a hacksaw and welded it at the proper new angle... It DOES help to be a bit imaginative and resourceful to do this, and proper tools are a must as well - it's not a BIG project, but not a simple one either - took me a bit over a half a day to install - oh, you will probably need a new '93 fan shroud too - another $25 or so from DC - depends on whether you want to try to adapt the old one or not, but the '93's offset the fan differently, and it was easier to buy the '93 and then modify it to fit the '91...
Good luck...