Hi Priesty, I'm pretty sure that you won't get a lender in the UK to give you a mortgage on this property as they won't be able to take a legal charge over the property. Your best bet would be to get an equity release loan on your existing property (assuming you have one that is) otherwise I really don't see how you are going to be able to do this. Even trying a Bulgarian bank you will run into problems as you are not resident there.
As hectic says, getting a UK mortgage to cover an overseas property is difficult. We are thinking of buying a place in the US and we are having to go through hoops to get one. We have been told its possible but most people raise the money here (through equity release etc) and pay cash over there. We looked into Bulgaria but we want a holiday rentail place and were advised that the only ones that'll make money are the ski lodges? Good luck tho. (Do you need a Bulgarian Bank Account?? We needed an American one for the US)