Buying Mirabelle Trees

We are trying to buy a Mirabelle tree. Friends in SW Germany grow a wonderful variety of Mirabelle. Locals can even rent a tree in the village orchards for a year and sell the produce. The Mirabelles are small, round, pale yellow and bursting with sweetness, so are perhaps the Nancy variety. However, when we bought a Mirabelle minaret from a UK dealer, it produced sharp-tasting greengages of a normal plum size. So, we would like to know where we can get the 'real thing' in the UK, preferably as a minaret. Any suggestions? Thank you!