Hiya, I`m also in Scotland! I agree with the previous members about Pets At Home`s adoption area, but if you have a large purpose build habitat, it may not be wise to house a pair together in case the cage allows them to become territorial if it has different levels or areas.
You could go for a single Russian dwarf or a Syrian. Roborovski are very speedy little things so if you have never had one, you may want to consider the habitat you have first as robos are not good climbers.
Chinese hamsters are good climbers are love digging. pets At Home usually have Chinese hamsters in their adoption areas but these hamsters are more mouse-like and shyer, so it depends what sort of personality you are after. Good luck with your search.
Oh and try Gumtree?