Man this is a tough one.I have a "Shaftshooter"(router motor style shaft maker"That allows me to make my own shafts at whatever length I want.It would be a good option for yourself.The problem is,you have to have really good wood to start with to make good shafts.
My advice would be to get intouch with Steve at Surewood shafts.He would be a great resource for you in getting really good shafts that are long,straight,and tough.Also,I have a 6" and an 8" chunk of 2512 aluminum arrow shaft left over that fits over 23/64ths wood shafts that can be used for footing over woods that you can have for your experimentation.If you need them just give a shout and Ill mail them to you.