There is a centre in Kavarna - you have to have your certificates with you - all dives available ! Sea horses in the sea too ! Sorry I left the contact details at the house - but the guys always seem to be around !
Hope that helps !
If you do a search there was another thread on diving running over the summer !
Sveti Nikola near Rousslka on the Northern Black Sea Coast has a Dive School. From 1 Day to 7 Day courses. English Speaking. I would recommend you based yourself in Kavarna...... or the Rousallka resort which is a lovely place ( as resorts go )