Here's one for you. Snap in center cap with Olds rocket emblem for SSII/SSIII wheels 73-88. The emblem itself is more for the G-body non-raised style rocket.
The 442 center caps are discontinued, but still stupid money. Set on ebay for $470-ish shipped plus tax for a set. Real GM ones, not the Chinesium.
GMPartsGiant.com offers the great deal for genuine GM parts, 552293. Wheel Cover Center Cap for $94.88. All parts are backed by the GM's warranty.
www.gmpartsgiant.com
GM list price $141.85. EACH. That's $567.40 for a set of 4!!!!!!! (43 years ago they listed for $10.45 each)
Cheapest I've seen the repros were $55 each.