I'm a big G&L fan, but you are correct they are difficult to source here in the UK. I took a punt on an ASAT solid body and got it shipped from the states after seeing it on Talkbass and doing a bit of research. All in including shipping and tax etc. It worked out either cheaper or the same as the prices here, but of course they did not have one like that over here.
Best thing i ever did, i have gone on to own an L1500, which is their take of a stingray and now and ASAT Semi-Hollow.
Like Gaz says they are some of the best made and sounding instruments you will find for the price anywhere in the world, yes he moved his on as he preferred a Fender sound which is cool, but its not a love or hate type of bass, you will either love it or really love it and not want to let it go.
Quick look on the internet there are a couple on gumtree and ebay, and to get the neck specs then its on the G&L website.
If its a defo P Bass you want LB100 is the classic sounding one, SB-2 PJ but you still get a Ptype sound, but with versatility, SB-1 is a P bass on major steroids.
If you are going to take the plunge bear in mind they are 'hotter' pick ups than most other basses and the controls both volume and tone were designed to sit around 75% at max.
The only negative side is that if you do make a purchase from wherever and you want to move the bass on, you my have to be patient because of the reason you stated that its not big in the UK, despite being fairly big across the pond and fantastic instruments.
Good luck and let us know how you are getting on