Indeed, that's the main problem. A group of providers who are very much wanting this to happen should probably get in contact with each other. Coordinate a few different days and times. Then post a thread, like this!, asking for interest. From this created thread you screen your clients (and providers?), discussing amongst yourself who you think would be a good fit and discreet. For some of the more established clients, suggest a +1 for them to possibly invite (again, another client). Sure, no hobbying has to take place while at the park; but maybe something can be setup for when you get all clean.
Then again, maybe that's being overly cautious. If you don't care or have little to worry about, then just blast a day/time with a general meeting area and have at it.
Edit: Oops, missed the last Honey Davis post which says as much. Haha