Hi if you look on the northern newfoundland web site they give a list of water training available, the nearest one to me (Yorkshire) is in Rother Valley Country Park, I know that they also train Leo's there. Sorry not sure of any specific water training for Leo's but it may be a good starting point.
If you go to www.leonbergerstudbook.co.uk and look under LCGB working tests, you should find all the info on water training there plus contact numbers :) We go and its great fun :)