I'd love to try it too, but even the local farms that have it are expensive - it's a pity it's no longer the food of the poor! I think I shall visit a restaurant next Christmas where it is on the menu. At least if I didn't like it I could probably get something else instead.
You can by a goose breast frozen on-line although it seems to be out of stock with this company at the moment:
https://www.finefoodspecialist.co.uk/magret-goose-breast-frozen-350g/