Hi Michael,
I would not recommend this wood for mast construction. What you need is clear straight grained wood, preferably not treated as the treatment effects the gluing reliability. The wood shown in their photographs has numerous knots and would not be strong enough for mast building.
I would suggest trying to find a small independent sawmill that will select the timber and saw it to your specifications. When I lived in England I was lucky as there was a local sawmill of this type near my home in Bewdley, Worcestershire. I also lived in the middle of the Wyre Forest and could select trees and buy them directly from the Forestry Commission. I got enough Norway Spruce to build the solid wood masts for a friend's 55 foot ferro cement ketch on one occasion.
All the best in your search.
David.