Glass layed down on a 45 degree angle to the stringer produces a stronger board and a more flexible board. Who sell this? Is is possible to improvise? Imagine bias S-glass with epoxy resin. Stop slinging shit, Rob Olliges 
We did a lot of boards this way in the past. Positives and negetives we encountered were: It was stronger but as you said, more flexible. Very light boards were a bit too flexy. Heavier board were alright. You need to glass two layers on both sides, one at 45º and one at 0 - 90º. That way you have what is known as tri- axial which we found to be quite strong and durable. Laminating on a bias is difficult because you have to work in line with the cloth fibers. You get wrinkles if your sqeegee work is end to end. 60" cloth cut on bias does up to about 7’ as I remember. You can stretch it a bit too. We did find 72" but never bothered to try it. Probably would have made it to close to 9’. There are also some double bias knit fabrics available but the weights of those are a bit much for surfboards, even EPS/epoxies. We did some sailboards with it with positive results. We did quite a lot of boards where we made the first deck layer bias. Probably helped with brealage but we soon after started using rail channels which were more effective.
bias cloth is good stuff,but you can take reg.cloth trun it so it is 45 degrees to the stringer and it work great…note!!! when rapping your rails start at the nose and work to the center then do the same with the tail…start at the tail and work your way to the center…sounds hard but it’s a piece of cake!!! ET
ET has glassed more boards this way than anyone I know of. I’m bettin’ that this is some good info.