Here is a list of suppliers that offer kit for sale. I will try and keep this updated as and when I find new reputable providers. This supplier list was taken and derived from the very useful, extremely helpful and considerate community setup on FB titled London / UK Production Sound Dept. Check them out!
Other useful non-specialist places: Sound Exposure, Canford (owns Panamic), Visual Impact/O-Video (Hire, Sanken replacement), CVP, CPC/Farnell, Studiocare, Studiospares, Digibroadcast, HHB, Aspen Media (distributes AETA), Amber Sound (Countryman distributors, RTS, PA systems), Acre Jean Drape hire (drapes, unsurprisingly)