There really is only one tire that perfectly fits the RCR 917, and looks the part, and that is the Avon tire.
RCR has these available, and they can be mounted and balanced on the selected wheels on your kit order.
Prices vary depending on the cost of materials, the dollar/pound exchange rate, and size. Call the factory to get up-to-date info and best fit for your car as ordered.
The sidewall can also be painted with the AVON name to look as original, or left all black for stealth.