Midwest Industries recently posted up their MLOK side rail for the KRISS Vector. No mention on cost or when they will be available.
I like them for how smooth they are. My only issue is that it is a single MLOK slot. This limits your options of what you can put on it. It is possibly only for mounting lights. I cannot think of an MLOK laser. So if you were to mount a laser, you would need a picatinny rail and it would not make sense to add an MLOK Picatinny rail ontop of this MLOK rail.
I think KRISS Arms should redesign their polymer lower and remove the threaded sockets. Then mold in MLOK slots like how CZ USA did with their Carbine Scorpion handguard. There is plenty of room in the lower receiver to allow for MLOK slots.