The only plug that I know of to the transmission on the passenger side is the Vehicle Speed Sensor. Did it come from the differential housing?
Check out this thread, post #17
http://www.grandprixforums.net/f81/gm-delphi-packard-connector-part-numbers-1514-2.html
If you still need a plug let me know, I have a few of them as well as speed sensors if you need that also. You will be able to order a new plug from the dealer also but expect to pay in the $20 range. Either way as mentioned above you will need to cut off your existing plug and splice in the new one and soldering with shrink tube is best.
I didn't look yet but i can look after work or how much for both mabey i will get just in case..Do you need the speed sensor in the trans also or does it look ok?