Craig, I don't think taht any Bulgarian ski resorts are open then to tourists booking through a travel agent. You could however do a DIY holiday but be sure to check the snow conditions before arranging it. Saying that, March is usually a good month for snow conditions.
Bansko. Was there last year about that time. Sno w was great, weather nice and warm. Perfect spring conditions. When booking that time of year best to book last minute.