The Ryfylke museum should have copies for sale. I do not know if they ship overseas, but send an email and check how payment could be arranged etc... http://www.ryfylkemuseet.no/index.php/butikk
2nd and 3rd option would be the local bookstore and the Suldal muncipality, who both should have the book for sale: http://www.bok-it.no/sand
You may like to know that a new local history for the Suldal Valley is under production. Suldal kommune has long employed Ernst Berge Drange to write local histories for all parts of the county. He has already completet 3 volumes for Sand and several volumes for Jelsa and Erfjord. He has been working on Suldal for a while, and the first volume should be forthcoming.
We are often at the museum and bookstore in Sand, but we have not seen copies of Hoftun's book for a while. The book was recently auctioned at QXL and sold for kr. 850. You might also contact Suldal sogelag for suggestions e-mail: suldal.sogelag@gmail.com