There is an SAE handbook out there that describes the properties of aviation fuels in great detail, and includes distillation curves for all of the standards. From memory (which isn't what it used to be), for combustor research purposes JP-8 and JET-A are quite similar; both are low-vapor-pressure (low cut) kerosene-like distillates. You shouldn't have any trouble getting some Jet-A from a local airport's aircraft refueling service, just bring a 5-gal. container and talk nice.
Getting military-grade fuels is, has been, and always will be, difficult for the average civilian. If you are engaged in a military contract, you should be able to work through the system to obtain what you need, but good luck -- it took us more than 2 years to get a sample of JP4 via "official channels". The un-official channels worked much more quickly.