Update from Graham a little while ago.
"The XR in 17" were a special batch made to order when we ran the SOA cars at Pikes Peak in 02/03. Some were sold on after the rally but no more were made after this.
Your best bet would be to contact Pirelli USA and see if they can get any made."
So, looks like the $300 per tire from the UK is going to be our best bet. Thanks Matt.
If anyone else planning to run Pike's Peak in Open Class that would be interested in going in on some of these from the UK to save on shipping costs contact me directly. For those who don't know, a portion of the upper mountain is said to have been paved. 2-2.5 miles past Glen Cove area. So that's potentially the first couple of hairpins in the Ws on the mountain and a total of 4-5 miles of tarmac this year.