I haven't been able to find anything specific to hamsters, but these places were listed on a rat forum so might be worth trying? I've got no idea how old the listings are so they might not even be running anymore. It's also worth looking on Preloved and Gumtree for your area.
DEVON
Ratty Haven Rat Rescue, Exmouth, Devon, has a number of rats for rehoming. If you can offer any of them a loving home, contact Siobhan Learnmonth on 07866-701311
Woodside Animal Welfare Trust, Elfordsleigh, Plympton, Plymouth PL7 5ED. Tel: 01752-347503 Open 1pm - 4pm apart from Wednesday. Phone ahead before visiting. Only rehome rats in local area and they check cages.
Animals in Distress, Biltor, Edgelands Lane, Ipplepen, TQ12 5QG
Tel: 01803-812121. They really need homes for their many rats and other small animals.
And this little guy
http://www.rabbitretreat.com/showthread.php?tid=3449
has probably gone, but it's worth contacting Exeter RSPCA as they clearly sometimes get hamsters in.