I was able to find a NIB LH Ruger Alaskan in 375 Ruger. The price was right so I grabbed it. Oddly enough it appears to be a non-cataloged version with a grey laminated stock which looks very similar to my LSS rifles. According to an internet article I located, the grey laminated version was produced in very limited numbers before production was halted.
New brass was much easier to locate than I expected and dies were readily available too.
The 375 Ruger kicks like a mule so maybe the 375 RUM wasn't the best idea to begin with.