I would say they are harder to find since they are one per case so at 10% that would be one every 10 cases. I don't know about where you live, but around here you are lucky to see more more than a couple of the same case.
When the second series Street Freaks came out in the # cars I desided to only collect the rubber tire versions, boy was that a tought set to get! Then came the Zingers, and I wasn't going to get any of them till I saw them on the pegs, changed my mind, decided I would get anything I coud get Plastic tires or not !!
I have them all up to 375-13 and I have found 6 with rubber tires, not counting the PMD Cuda & the WW4 Camaro and I have one Camaro w/red stripe #375-10 for trade ! I'll trade the Camaro for the GTO if you like !:thumbsup: