auntog, adding to Auld Codger's comments - I think if you were able to get an appointment with a private oncologist in the UK you would need to have copies of all the scans, blood test results, reports and medical notes, and presumably these would need to be translated from Bulgarian to English. Next week may be a bit too short notice to get all that in place and arrange an appointment.
However, if it is possible, and you only want a second opinion or reassurance that the treatment still available to him is the best you can get then Google is your best bet - look for oncologists that are involved in active research or have delivered talks on prostate cancer at recent British Institute of Cancer Research meetings / conferences or similar.