In this case AliExpress is your friend. They have all kinds of options to solve your problem. These Foster fittings come in different threads as well, so you have to understand the differences. Personally I absolutely hate using BSP anything. The thread form is 55 degree as opposed to 60 degree for everybody else. BSPP (British Standard Pipe Parallel) does not thread seal. BSPP base seals, so theses fittings require a nylon or fiber washer at its base. When you look for a male 5/16" Foster fitting, they all come with a directional valve in the fitting. That is not a problem if you don't want that. Just use a pin punch and push from the filter side and it just pops out. Further most charging whips (hoses) seem to use 1/8" BSPP on the ends. You can make up any combination you want by just changing the end fittings accordingly.