Your best bet is to either buy urethane motor mount inserts or fill them with urethane yourself.
Simple inserts:
MR2 urethane motor mount insert page
Replaces stock rubber completely:
Twos R Us - Parts for Toyotas from Club MR2
For a cheaper option, you can buy urethane (usually Shore 75-90a, depending on how hard you want them), from
McMaster-Carr and do these yourself. Just remove them- I removed the front and rear, then the left and right side, and left a jack under the engine for the night. After you have them off, you just seal one side with duct tape, and fill them, then let them harden for like 24 hours.