Trafford Park Costco said they'd supply them, but only when I'd told them they were to be fitted to some spare wheels for track use only. Guess it's who you see on the day. or rules have changed. I hope not the latter.
R1-Rs are getting some bad press as track tyres, they overheat and go greasy, epic fun on the road but noisy as hell. 888s are grippy as hell, but they've lost the USP of being cheap, so there's better alternatives. Kumhos and Hankooks are very well thought of, wear better and have stiffer sidewalls.
Do you want something to just use at the track, or are you wanting to drive to and from there also? If they don't have to be technically road legal (although these are E-Marked, so its a grey area... but probably not worth risking), there's a load of brand new Kumho cut slicks on PHeads at the moment in 22/40/18 at around £70 a corner from a defunct race series.
And lastly, having used both F1 assyms and PS2s on the track, the latter are a bit better. The F1s lose grip towards the end of their life, where are PS2s keep going till bald. The F1s also rumble the tread blocks when hot, which is annoying as you can feel them squirming.... but F1s are a lot cheaper, so if you forgive their faults and just race through them, then they'll do fine.