Unfortunately Bulgaria is not an easy destination for travellers with disabilities. Uneven and broken footpaths pose challenges, and ramps and toilets designed for disabled people are few and far between, other than in a handful of top-end hotels in Sofia and other big cities. Public transport is not generally geared toward the needs of travellers with disabilities.
One organisation worth contacting is the Center for Independent Living (www.cil.bg) in Sofia.
Download Lonely Planet's free Accessible Travel guide from http://lptravel.to/AccessibleTravel.