I also tried to find someone selling a cheekpiece assemblys I knew what I wanted and had seen many stocks with them fitted but no one knew who sold them . in the end I found a company in the USA ( the warner tool company ) who make them . but I will need to have it fitted into my laminated stock but im lucky Im friends with someone who builds guitars for the rich and famous who will fit it for me . or have a look on UKV varminting there is someone on the site who does this type of work maybe he can help .
I watched the video too, what a crappy add on it is, the plastic injection moulding tool surface has not been grained for it to match the Brownings stock and I find that it looks awful as hell.
Browning get the tool grained to match, there are many companies offering this service
if you want an adjustable comb fitted to an existing stock id send the stock to Simon at doveridge, he's completed a number of comb conversions for fellow clay shooters and his work is very reasonable, he's also quite good a turnaround times. its about £190 including the hardware. http://www.doveridgeclaysports.co.uk/our-resident-gun-smith/
PS I have no involvement with Simon I just rate his work..