Go for it.
British cuisine is a little more than Marmite & brown sauce.
Promote yourself with the indiginous Bulgarian community.
I am sure that many Bulgarians will be delighted to have an opportunity to sample British fare, which includes a huge range of attractive & tasty manufactured treats with very long shelf life. A few have already been mentioned in earlier posts..
Bulgarian sweeties, just like all foreign sweeties, are of a tiny & miserable range when compared with the British. This is sweeties, remember, not high class confectionery which in most places is made far better than the British can.
You could negotiate with local baker to make British speciality cakes / pastires with a decent shelf life. Welsh cakes, eccles cakes, lardy cake spring to mind.
Local make will mean local pricing which will mean good local sale price. Local butcher to make British style speciality sausages.
Import is not your only option.
Sensible bulk sourcing & shipment should enable a decent mark up on imports.
Good luck. I hope you enjoy your venture & make some money.