I think I know why Proctor knew the address. There was a scene before the Blue Oyster fight where Proctor is showing Mauser the pictures of 'Fruits drunk at the bar' that he was told to get. Then Mauser tells him that he wanted pictures of the 'New recruits drunk at the bar.' So my guess is he just looked in the phone book for the address of a gay bar and since it was only a day or 2 since he went there he would remember it.