Donald et al,
Try http://www.photowarehouse.biz in Oxnard, CA
I never did business with them (as I live in the Netherlands) but I reguraly come across there name when people are looking for film for largeformat camera's (11x14 and upwards).
Since recently they have above website and it lists high contrast ortho film.
Also look at the graphic arts materials as I expect that several products would fit the bill.