250E/250N gearbox karts - where to buy?

[gee_fin]

I've been out of the game a while but looking to buy a 250 gearbox kart. Tried the usual places (karting.co.uk marketplace, here, eBay, etc.) not really having any luck. Can anyone recommend a more productive place to be looking? Would consider both single and twins (250N/250E).

Cheers,
Graeme.