There are 200 hits on UKP when you put "Harrow" into the search box. Fortunately, as some members do review the girls they see (!), you should find something there that will help you in your search. You will need to do it in combination with AW to find which ones are still currently available, but surely it's not too time consuming, and finding a girl in this way can be fun too.....
PS - Try Dilem - she's very close to Xena and Nikki's place and charging £100 p/h at the moment