Of course, I have no idea the legal entities that you have to deal with, but, I had the thought that perhaps if you put a scientific spin on your project that the authorities might take a kinder view of your project.
1) there is a fascinating Girandoni type airgun in the Cortina d'Ampezzo town museum. It is inscribed with the name of Girardoni's assistant and has the fascinating feature of variable power (full -med - off) by use of an lever on the left-side plate. This is the only known example of a variable power Girandoni and the variable power function has never been demonstrated.
2) Amazingly, we still don't have a video of a Girandoni discharging when the hammer is decocted and the tank is still attached and pressurized to some degree. We can see people talking the sequence through and giving their opinion on what will happen but nobody has yet had the guts to actually demonstrate this well-known inherent danger of this battery type. This is almost without question the safety problem demonstrated by M. Lewis at Bruno's Is. with his Girandoni. Famous, historical incident that has never once been demonstrated on video.
If you think that selling your airgun project ask a scientific/educational project to the authorities might make a difference, I would be happy to help anyway I can. I'm reasonably sure that I understand how the variable power feature works and it would be wonderful to get a real world demonstration. I could also put together a paper on the M. Lewis Bruno Is. incident, along with a description of the history of the safety "de-cocking" feature found on later Girandoni's, including the Austrian and English variations of this safety feature.