From White Racing Products:
http://www.whiteracingproducts.com/
Insert, Power Seat Triangle Bezel R/H 12514822
L/H 12514823
Not cheap at ~$35 each
From Corvette Central (looks not available)
3519. 12514822 594360 *USE 484510L* LH TRIANGLE BUTN
3520. 12514823 594360 *USE 484510R* RH TRIANGLE BUTN