It would be a case of researching which ones you liked and making sure you can match their needs. A lot of them need very soft water - which unless you are blessed with soft tap water would mean RO water.
Once you've decided which species you are interested in you could try something like Tropical Fish Finder.com or Aquarist Clasiffieds which are sometimes good sources. Which area of the UK are you from? North South etc? Dont need to be too specific I'll probably be able to point you in the right direction if you are willing (or rather alowed) to travel a little?
Wills