I've gone to London several times as well but it's always been by request for a particular client. If there is a lady in particular you wanted to see let her know that you are interested and you might find she is able to accommodate your request to travel. Every lady structures these types of travel requests differently, some will charge an additional travel fee, some will request a min. number of hours, and sometimes a deposit or references are required.
If you don't have anyone in mind but rather would like to see ladies touring in your market then you might want to gather a few like-minded gentlemen on a board then let the ladies know that as a group you are interested. If you formed a "London Tour Group" then ladies could easily test interest and post their travel plans for the group. This option would demonstrate to the ladies that their is a market and interest in your city and would allow for shorter appts (30min or 1hr) rather than having to book an evening date which you usually have to do in order to have a lady visit you specifically.
Oh and as to why not... well the London market isn't nearly as big as Toronto, nor is the marketing as centralized as Ottawa. The advantage to those markets is you can easily reach your audience to ensure that you have secured your min number of bookings. The London market is spread across several boards which requires a greater amount of time and money in order to advertise a tour, reaching your audience is a lot of work and there isn't a guarantee of interest.