Looking for advice on replacement. It's a larger than typical diameter. Even the ncordinance.com repro. is slightly undersized.

Ser#255xx range. Came with white line spacer and a black grip cap, the cap appearing shrunken in diameter with age. Would like to put the original parts away, and fit a simple black plastic cap (or nicer), but not having luck finding one. Any suggestions?

How about a nice contrasting piece of real ebony that can be fitted and sanded to size? I am sure there are some stockmakers etc. that would do that kind of work if you do not want to attempt it yourself.

Have you checked Brownells?

https://www.brownells.com/rifle-parts/stock-parts/butt-plate-parts/grip-caps/index.htm

My preference is to not permanently alter the grip. Didn't have any luck with Brownells. Been kicking around the idea of a piece of ebony (or black bone/horn/antler) maybe 3/16 or so, fix it to the grip with a single screw in usual fashion rather than epoxy it. The profile it, the options being square-shouldered vs. round/countour the whole ebony cap, realistically, unless someone has another suggestion.

Did you try Numrich?

The other one to look at would be Hoosier Gun Works.