Yo Dick

10 foot long - you lucky devil. We only get 8' long sheets here in New Zealand. I wouldn't bother trying to find any 12' stuff. I would just scarf join two sheets to make the length you want. Scarf = 1:8 beveled edge on each sheet that is to be joined and then you glue them together.

It is easy enough to get a good scarf. Mark and then butt the edge that you are going to plane so it is directly over the edge of a table (so it is fully supported right to the feather edge) and plane away. Do the same for the other sheet, rough up the faces, glue and hold everything inplace while the glue dries.

If you are really on the ball you match the sheets up so the grain is similar and you probably won't even notice the join - but that is easy for me to say, especially since I butt joined all the panels for my guillemot s&g's.

Good luck

Pete