Grendel went under for some reason. Kel-tec CNC is not the same company, though the same guy that designed the Grendel designed the Kel-Tec P11. They are a completely different company than Grendel, not just a reincarnation like so many gun companies that go under. I'm sure some of the players are the same, but the success of Kel-Tec would seem to indicate there is some difference in the leadership of the company. I don't know why Grendel went under, other than all they offered was just a small .380 and some .22 I believe at the time the CCW wave of laws hadn't occured. Small market, wierd gun, lack of other products, etc.
The Grendel .380 is pretty big for a .380. It's not much smaller than a P11, which is 9mm. It's sort of a similar set up in that it uses a plastic grip frame with a metal insert, and steel slide. There was no detachable mag. If I'm not mistaken, you loaded the mag through the top of the gun with the slide locked back, like the old Broomhandle Mauser. There was some sort of stirpper clip set-up I beleive. That feature in itself would pretty much doom any design. It's been a really long time since I held one, so I'm not sure on the details of the gun.
I don't know anything about the product numbers, so I don't know what a R31 is. Your best bet for spare parts is probably to contact Kel-Tec and see if they know of a source. Check the KTOG (Kel-Tec Owner's Group) for info as well. They have experts in these guns. There's bound to be a Grendel owner over there.
It's not worth much sorry to say. Figure there's really no practical reason to own one over a 9mm P11, so the price would be less than that model. That's pretty low in itself. There's no collector status involved with the Grendel.
www.ktog.org
Ross