First off, take your Mazda dealer's phone number out of your address book
. Call Ray Crowe at Malloy Mazda - 888-533-3400 - tell him what you need and if Mazda has it, he'll get it for you. He's REALLY sharp and knows RX-7's backwards and forwards, will give you a fair price and free shipping.
If Mazda doesn't actually make that part for whatever reason, here's a trick I've used on many 2nd gen RX-7's. Go to Wal-Mart or a hardware store and look for the feet you stick on the bottom of chair legs - they have hard plastic stick-on feet that are about 3/4" diameter or so. They work GREAT for that application, last a long time, and if it accidentally comes off you can grab another from the pack and stick it on.