"Dragon breeding was outlawed by the Warlocks' Convention of 1709, everyone knows that. It's hard to stop Muggles from noticing us if we're keeping dragons in the back garden - anyway, you can't tame dragons, it's dangerous. You should see the burns Charlie's got off wild ones in Romania."
-- Ron Weasley (PS14)
There are presumably dragon reservations all over the world, hidden in the mountains where Muggles are unlikely to come across them. However, we only know of two specifically: one is between Kopparberg and Arjeplog in Sweden (FB); the other, in Romania – where Charlie Weasley works (PS6) and which, most likely, Harvey Ridgebit also established (JKR).
After retiring from teaching Care of Magical Creatures at Hogwarts, Silvanus Kettleburn frequently visited dragon sanctuaries; this resulted in him repeatedly needing replacements for the magical wooden limbs he received from Albus Dumbledore as a retirement present (Pm).