I've been getting mine from
Concept Racing. Not sure if he has any in stock right now after the recent robbery though, no doubt he will be able to help you though
I was shocked at the cost of a pair of stock tyres, but they work brilliantly on dry Astro, better than Goosebumps with and the foam inserts that come with them!!
The J Concepts Rulux wheel is also better value for money than the stockers!
[edit]I've been using M2 Proline Calibers on CMCC dirt track, now most of the dust has gone, they work brilliantly, wear isn't to bad either, they should last for 3 or 4 meetings on the very abrasive surface. Got some Bowties to try on the rear as well, just waiting on some V3 foams...[/edit]