It's no more complicated than valuing the power supply for an electronics device, the simple answer is you can't do what you want with what you have.
Those kinds of compressors weren't meant for continuous use, you're trying to operate the device way outside of it's design paramaters. The motors stops at that pressure because that's the ultimate limit of the mechanical system at the motors given voltage. Increase the voltage and the pressure will go a bit higher and the motor will heat up and destroy itself, even if you don't increase the voltage the motor is eventually going to fail from overheating because they weren't designed to be run for any length of time at their max pressure, it's only supposed to fill up a tire and then it's done, and then it's supposed to be let to cool to room temperature before it's used again.
30psi pneumatics are going to be really weak anyways, you should be using a small pancake compressor from a home improvement store or try to pick one up used locally, they're not expensive and will easily handle 60-120psi of pressure generation, but you have to worry about how much volume you're going to need as well, that's a completely separate issue.