The production numbers for the 992 must have been much less than the 979 as the 979 forks rarely come up for sale, but I have seen them once in a while at eBay. You just need to continue to be vigilant with your search.
Good luck in finding one.
By the way, am I correct that the 992 steerer tube is a bigger 1 1/8" diameter size? I would have suggested you go with a 979 fork first to get the bike ridable while you search for the 992 fork, but if the steering tube diameters are different then you don't have that option. You can always find an aftermarket fork with the proper size steering tube, Maybe the carbon or aluminum ones made by Look?

Chombi