They are out more often than not, at least they have been for the past year or so. They sell out fast.
For the money (especially if you get them on sale) they are a great optic for the price, I ran one for several hundred rounds on an Ar with no problems and it held zero perfectly. Now they are on .22s and I still like them a lot.
Word is on arf.com that they will be getting another batch any day now. They are still a relatively small buyer so they have to wait for the factory to get back around to them. They are looking at other factories but PA did some major vetting on the first one to ensure the quality.
However, if Vortex would make a more AK friendly Sparc (lower mount, emitter to the side), I wouldn't be waiting on Primary Arms.