There are many answers to this question, but let me try to address them all.
1. I thought for a time that there was going to be an event last weekend, but things fell through on that one.
2. The next event within an hour or so is
The World Geo-Gathering which will take place in Wyandotte OK (near Neosho MO) at the site of the D-day adventure park from 16 to 19 July. Early registration has ended, but you'll still be able to register at the event.
3. Rhonda and I have been talking with debmitc about hosting an event in Tontitown this fall. I have some ideas and have spoken to Chuck Walla about them. Look for a posting here in the near future for a breakfast meeting to discuss this. We won't take this on on our own!!!
As for your original question "How often... ", Rhonda and I have tried to make sure there's a meet and greet at least a couple of times a year. We've talked here in the forums about having something once a quarter, but nobody ever seems willing to step up (excluding the breakfast in Van Buren == thanks geniegill)
Finally, the cachers in Springfield MO are always having an event for one thing or another. Keep an eye out for events up there.
Hope this helps, and hope it gets you excited about helping out with the fall NWAC event.