In one game it took me 12 tries to win any Concept Car, and it was yellow. The next 2 races won me two more yellow Concept Cars, and then the next one finally won the purple Concept Car, completing the set of four prizes for the UKvsUS series in that game.

It seemed to me that that game would get stuck in ruts of winning some particular prize for some event. But considering all my games overall, the purple Concept Car seemed more common than the yellow overall. And it sort of seemed like the "rare" prizes were more common early in the games than later.

Code:

80-85 [R]Cerbera UKvsUS sw45to24,20,19,9,8 blueRX7(1/4)i
218-223 [R]RT/10 UKvsUS sw45to24,21,19,11,5 blueRX7(dup)a
224-229 [R]RT/10 UKvsUS q6SS11 1st45to25 blueRX7(dup)a
230-235 [R]RT/10 UKvsUS sw45to23,20,18,13,6 blueRX7(dup)a
236-241 [R]RT/10 UKvsUS sw45to28 blueRX7(dup)a???
248-253 [R]CerberaLM UKvsUS sw45to22,22,20,11,5 blueRX7(dup)i
272-277 [R]CerberaNOT UKvsUS sw45to26 greenRX7(2/4)i+a
278-283 [R]CerberaNOT UKvsUS sw45to28 greenRX7(dup)a
296-301 [R]RT/10 UKvsUS sw45to24,24,14,13,5 greenRX7(dup)a
309-314 [R]RT/10 UKvsUS sw45to25,19,19,11,6 blueRX7(dup)a
315-320 [R]RT/10 UKvsUS sw45to24,24,14,13,6 greenRX7(dup)a
321-326 [R]RT/10 UKvsUS sw45to26,22,14,12,6 yellowConcept(3/4)a
327-332 [R]RT/10 UKvsUS sw45to28 yellowConcept(dup)a
333-338 [R]RT/10 UKvsUS sw45to26,19,18,12,5 yellowConcept(dup)a
347-352 [R]RT/10 UKvsUS sw45to22,20,17,14,7 purpleConcept(4/4*)a!

Viewing a collection of results from different games, I got...

12 green RX-7

9 purple Concept Car

8 blue RX-7

3 yellow Concept Car