Dim Sum - to get and to eat
If you stay in bigger cities, usually there are Chinese supermarkets. Most of them sell frozen dim sum. They are uncooked. Just follow the instructions to cook them. It's cheap when you buy and cook them yourself. In fact most Chinese restaurants use the frozen ones.
But if you are travelling, then you have no choice but to go to the Chinese restaurants. I seldom go to restaurants for dim sum because they are expensive and sometimes not very nice. I try to make a few types if I like to eat. I have not tried any in London yet though I travel there quite often. When I'm in London, I like to go for Malaysian food or Chinese roasted duck rice.