I think they stopped making Yoko A539's in 2007, that's when we stopped using them in the race series as they couldnt supply them any more. Replaced by C-Drives. Both were useless in the damp/cold.

Have you have a look on camskill's website to see what they can supply?

There are some quite good tyres from Hankook and Falken that should be less than £50 each in the small sizes. You may have to go 55 or 60 but will make not a lot of difference.