You'd have to find a well informed "construction supplier" in your area. These would be the type who sell materials to insulation and roofing contractors. The OC you are looking for is usually referred to as semi-rigid insulation around here AND is special order.
http://www.owenscorning.com/comminsu...s700Series.pdf
Unfortunately the local sources of 703 and 705 I found would be pretty useless to you but I was quoted a minimum quantity of 48 sq.ft. (6 panels of 2'x4) and 3" of the FR705 cost under 140$US (converted from $cnd)
Good luck...
Rob