I got mine at Maw online. I would not know where the best place to buy in the UK is, but this might help some

Here are the part numbers list for the TBA: Prgressive shocks
Here are some photo's: http://www.mawonline.com/photos/prog_412_series_shocks.gif

BA has Freak, 160mains, 44pilots, air mix3 1/2 to 4 turns, BUBS dresser dogs. Never had more fun on any bike - 2nd bike 2008 RIIIT