Forsythia, chanemeles (japanese quince), tamarix, philadelphus (mock orange) all grow wild here so do really well. Berberis, cottoneaster, butterfly bush (buddlea), spirea, cornus (dogwood), choisya, hebe, rhus and yukka. Clematis (is a weed here too) honeysuckle and climbing hydrangea are all growing successfully in my garden near Veliko Tarnovo.
There is also a climbing plant that is a bit of a thug climber that grows wild. It is beautiful with large orange trumpet like flowers but sorry I don't know it's name. Also russian vine another thug climber that grows 15 ft a year.
I have foundtwo garden centres round this area where most of these are available.