Up until a few years ago, A.G. Russell listed in their catalog a marlinspike knife that was Japanese in origin, with either black or 'coral' (red) Rucarta (A.G.'s version of Micarta) scales on a stainless frame. So far as I know, I think the only version available was with a fully serrated blade (I think it was AUS-8). Up until they discontinued that knife, I believe it was priced somewhere around $60 - $70. For a while, they could be found on eBay occasionally, although I've seen a couple that were OUTRAGEOUSLY priced ($200+), as they were innacurately described as either 'custom' or, in one case, as a 'prototype' (with no included provenance or documentation to prove it). Russell sold these for many years, so I'm certain they're not THAT rare.
The current versions listed in the Russell catalog are significantly more expensive and sophisticated, in both materials and design (frame lock). One offers a stainless handle w/440C blade in plain edge, front-serrated combo edge, or rear-serrated combo edge. The other is a titanium handle w/ATS-34 Ti/Al-coated blade (front-serrated combo edge only). You might've already looked at these newer versions on the A.G. Russell site but, if not, here are the links for those:
http://www.agrussell.com/ag-russell-stainless-seamaster-front-serrated/p/AGSAhhh118SSF/
http://www.agrussell.com/ag-russell-seamaster/p/AGSAhhh118TI/
I've been equally frustrated in finding (not) any details on the web about the older version. As far as I can tell, it's no longer listed anywhere on the Russell site either. Your best bet for info on A.G.'s older product line might be in finding some of the older A.G. Russell catalogs (also found on eBay occasionally). I think the earlier, less-expensive marlinspike knife could be found in catalogs at least from mid-90s thru maybe early or mid-2000s. I think I still have a good many catalogs laying around here. I'll see if I can find one that still lists that knife....
Edited to add:
I've forgotten that some of the older versions also came with smooth bone handle scales (nicely suited for scrimshaw). I just took a look at eBay and found a completed listing for one of these. I don't remember what A.G. originally sold these for, but I'd assume they were priced a little higher than the Rucarta-handled version.