I recently adopted a Robo from Pets @ Home. I kept seeing him there on his own for ages, so I took him in
I had a long chat with the manager and some of the staff there and the hamsters they have there for adoption are either ones they've taken in (sometimes dumped, in a box, on their doorstep during the night - disgusting I know) or they're the unsold ones from they're own stock.
There's a suggested charity donation of £5 (I donated £10) and that money goes to different animal rescue charities.