why dont you put letters through the doors of the properties you have seen that are empty, offering the landlord the chance to lease to a genuine tenant without the agents fees, im sure this would appeal to lots of people.....
have you called around all of the local agencies? if theres no boards they will still be on there books!
failing that the best thing you could probably do is chat to the neighbours of propertys, they have usually been friends with who ever has moved out, that person will have landlords details......
i wouldnt ever lease a run down property!!!!! at the end of the day you will just be restoring it for the owners benefit, if theres a particular premises you want that is run down, id strike a good deal with the costs and rent before even considering it xxxxx