has anyone found a way to make the fitting on the front of the combustion chamber i want to make a gun with the same design but cant find that part anywhere besides their website and its nearly 100 dollars there.

can you tell me what parts are needed for the fueling system i am working on a propane gun with the same design but breach loading and with a sliding barrel support and the only problems are with the fueling on account of the price i already have 2 other guns but they are both spray and prey.