You can rent dinghies at Albena beach but of course it's coming to the end of the season. Next year there should be more boats to rent and a small sailing school. There's nothing at Golden Sands.
I've been looking into sailing clubs, mostly they are places where a few people keep a few boats. The concept of a friendly sports/sailing club is very new here, the best one is in Nesebar.
However, we're trying to help promote sailing in this country. There could be a sailing club/school in Varna in the future.
I see have a house in Kranevo, so Albena is very convenient for you.
Are you in BG or UK at the moment