www.car-part.com for local junkyards.
you will want to get a tranny from a 92-94 SOHC model. the 89-91 models are the same transmission, but they're a bit weaker and prone to problems. I'm not sure if it's a computer or better parts issue, but the later trannies are better.
by searching car-part.com, you'll be pointed to the right one based on their menus, but just in case, you're going to want one with a VIN that starts with JN1
HJ-------, the DOHC model is JN1
EJ-------- and isn't compatible.