Okay, so I am not a lawyer, but do be careful.
I guess I'm not sure what pressure you are attempting to measure. Open air pressure of the waves around the engine? Wouldn't a series of load cells around the engine also tell you the current pressure wave ... well, pressure? The rupture disk would only tell you that you reached a certain threshold, not necessarily what that was or is until it does break.
I've seen enough of these things used on MythBusters to know that it appears they use suspended PVC contraptions that look like they have an aluminum burst disk at the end. My thought is that you could build an equivalent using a consistent-density metal, perhaps aluminum foil or other sheet metal like that. I suspect that the variances in the metal would make it an unreliable tester though.
I see that eBay has a lot of industrial surplus for "rupture disk" and "rupture disc". Perhaps you can find a bulk lot?http://en.wikipedia.org/wiki/Rupture_disc
Either way, good luck!