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. 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.