As you suspected the grips appear to be custom grips. They are nice in appearance. The correct period factory diamond magnas are not difficult to find either on eBay, GunBroker or other places. You could most likely get a set for around fifty bucks give or take ten or twenty dependent on condition.

On the other hand, plenty of folks would be OK with the current grips. You could use this as a negotiating point and offer at least a hundred less than the seller's asking price. This is, unless the seller has the originals. If it is mechanically sound, you will be OK at three hundred to three and a half.

One's home location often dictate availability and price. Around here, Model 10's are plentiful and I have bought three in the last year to include the one I posted in the picture. Then there two 10-5's with one in poor condition for $174 and a nice factory nickel for $222.

My 2 cents worth, but others posting in this thread have already offered different view points.

Good luck with it, and let us know how it goes.