14mm Piston Head

[Pepperisit]

I need a new piston head for my mp5 with the dirty army reinforced nozzle.
It measures 13-13.5mm inside of the nozzle. I am not looking for the rubber cup style that I have at the moment but instead the same style as you get in AEG's. For example I have the pdi winter head in my px4 (from a 5-7) but it is 14.5mm and is too tight to use that.

Does anyone know of any metal/plastic o-ring style piston heads that are around 13-13.5mm across?

Thanks in advance!