funnily enough exotic aquatic is just that THE AUSTRALIAN ADA GALLERY its a very high honour
he usually does have some for sale on the little water fall tanks on the left hand side when you enter the store. maybe hes out of stock at the moment
I would thoroughly suggest having a look at liverpool creek aquarium. they have a great range of plants(some quite hard to find elsewhere) and alot of information available in the item descrition regarding conditions and difficulty etc. http://www.liverpoolcreekaquariums.com/store/c18/Mosses%2FLiverwort.html
otherwise Subscape would be the other go to place for interesting plants :)"
Steer clear of java, subwassertang and riccia. They are very hard to tame and maintain especially long term and tend to work thier way out from your tying .
look into fissidans, pellia and rose moss (they all grow small leaved and compact and will grow and climb over the surface rather than out from it)
you could also try mini bolbitis. depend swhat look you were going for i spose
Best of luck!