Probably isn't one. They are held when somebody has the time and desire to host it (it's not a small amount of work). We've been averaging one every 2 years.
WHAT DO YOU MEAN?
IT's NOT A SMALL AMOUNT OF WORK. THANKS to SOME, the 2 I Hosted went very well i thought with all there help, and the other 2 i Attended seemed effortless, with the same folks helping in what ever manner they could.
WE ALWAYS HAVE A BUNCH OF GREAT GUYS TO DO WHAT EVER IT TAKES.