I just fixed a friend of mine'* 93 Bonneville today. I went to the local auto salvage yard and just searched through all of the GM large cars (Olds LSS, Olds 98s, Buick Park Ave., Cadillac Deville) that have the four rear subframe/cradle bushings (Grand Prix'* and the mid size cars only have two). I just found the car with the least rusted cradle, metal cups and bolts. I got some off of a low miles Cadillac Deville (probably late 90'*). It cost me $1.50 each for the four. I bolted them all up today and they worked fine.
Good luck, hope this helps.