There are regional meet-and-greet type events, if you are lucky enough to live close to an area with a great enough density of Young Scholars to attend one. Our next one is a couple hours gaming session at the library. If you meet someone that you "click" with through these, then presumably you could meet up for playdates with some of the connections you made there. The tools are there for online interaction between kids (the elists), but it doesn't seem to be really popular.

Zen Scanner gives some good examples of why asynchronous kids may not fit in well with their age peers. As another example, DD8 wanted to "play goddesses" with her friends, and assign everyone roles as Greek goddesses, but everyone else did not necessarily have encyclopedic knowledge of them all, especially some of the lesser goddesses. Girls who were old enough to have read all the Percy Jackson books (her initial source of this knowledge) were not necessarily interested in pretend play any more. Peers who are both the same age and the same intellectual level were a better fit.