Bruce, it used to be available through this site [www.mamut.com
] (As you can see from this page [www.mamut.com
] they still have "Våre motorskip"). I believe "Våre gamle skip" is out of print, but you could try writing to them, there's contact info at the first link.
Also, I believe it's available for sail at the Maritime Museum in Stavanger (it won't be listed on their website, but you can write to them, or call them)
If the above fails, try writing to Hillesland Books [www.hillesland.no
I'm not sure if any of these will ship books out of Norway though, but it's worth a try.