Wandafish, have a look in the post in Tank and Equipment " Our new Tank" . You'll see the size we bought for our 2 fishies, so you can have some idea how big a space they need. Eventually we'll get 2 more but this is maximum for this tanksize.
Hope this helps.
We bought it 2nd hand. Sure you will be able to find sth similar, just look arround, ask in your local pet shop, they may know too.
Look it up in newspapers, etc