From the Four Horsemen twitter feed:
"OSM waves 3 & 4 Alpha Phase waves FINAL 13 SETS up for sale tomorrow (Wed.) night at 9pm at StoreHorsemen.biz !! -FH-"
So there you have it-- just 13 sets remain! They're really good figures, so if you're on the fence just buy them.
Watch this page for ordering information. I like my set, so unless you plan to hold off for the painted editions, just get them.