So the nuts that the Polaris Parts guy said I needed to order arrived today, wrong nuts. Can't find a picture of what I need online or in the manual.
These little guys look like a thimble with splines on the outside and thread on the inside, and one end had a cap. You pound them into a hole in the frame until the cap seats. You screw the caliper bolts into these splined nuts. Anyone have a clue where I might be able to pick some up. The two that were in there can come out with your fingers, the splines worn down. Thanks in advance again, and again.....

 

Update: after hours of looking I found a picture of a "Rivet Nut" that is identical to what the brakes bolt into in the frame. Any idea where I can get fitment info? I've tried several parts houses and "rivet nut" returns no items found.

 

Think I know what you're looking for. They're called splined nutserts. Can't find em either on the frame,caliper mounting,or frame itself,but I believe they come with the complete frame? Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
Body Supply and Fastener Company - Fasteners, Assortments Kits and Bulbs :: Fasteners :: Threaded Inserts (Nutserts) :: Steel AVK Standard Threaded Insert, Large Flange Yellow Zinc
You can try Ace or any good hardware store. Just take one of the bolts and match the standard threads up. Worst case if you have enough room just add a lock washer and nut behind the frame.Get longer bolts if needed.Rivet nuts are similar but you have to have the tool that compresses these into the frame and "mushrooms" the fitting.

 

I went outside to pull one of the nutserts to take to the hardware store in the morning. I looked at the frame under a bright light and realized it has taken a beating and the holes probably won't hold the torque before the new nutsert would spin. Here's an interesting twist: The (wrong) nuts that arrived today are self locking steel split lock nuts (flex nuts). And, they are the correct size/thread to the caliper bolts. Rather than fuss with nutserts that may or may not be tight enough after pounding them in to withstand the torque, I'll take you last suggestion and use the flex nuts with a lock washer and call the job done. Too tired to try this evening, but I'll let you know tomorrow how goes after I try in the morning. Once again and again, many thanks. The lower motor mount is my last task, then time to get'er fired up!