24inch barrel in the uk.

hi people, ive been doing a few mods to my stealth recently and it is performing really well, i was jus wandering whether anyone knows where i would be able to get hold of a 24inch .22 barrel for it, from here in the uk?

i dont have a chrono at the moment so dont know exactly what sort of power im getting with it, would anyone be able to hazzard a guess?

ive done all the work to the standard valve shown in the thread in the quick reference section, porting and polishing, drilling it out. ive also got a brass hammer installed and a much stronger main spring, (dont know exactly how strong).

would i benefit from a longer barrel and can anyone recomend some good quality heavy pellets?

cheers

tom.