I've ridden in cars with them before and haven't noticed any odd vibrations or anything....
You can pick them up from most parts stores, the local Autozone in Ewing keeps them right on the shelf. GM rwd auto tranny mounts are pretty much all the same. There are a few exceptions, but not many.
Here is a link to a pic of one:
http://www.spohn.net/productimages/TransMt_big.JPG
- Justin