I'd start by speaking to a company that operate AS350's.
How about London Helicopters at Redhill, Elite Helicopters at Goodwood or Oxford Air Services at Oxford as three closeish suggestions. I'd avoid any so called (and self described sales gods) that have no knowledge of the type
Why are you looking? Private owner looking to just use the aircraft for yourself? Prospective owner thats looking to lease back some hours? Will you need help with hangarage and maintenance? Looking for an aircraft already on the G reg or do you require an aircraft on an alternative reg? Probably a good idea to consider all options from the outset.
I cannot think of any for sale at present, but feel free to PM any definitive questions you may have (if any) and I'll do my best to provide some practical guidance where I can.
FW