I doubt if this part is available for sale See part #2 on the diagram.
It's looks like a simple orifice, called a "choke" on EKTA.CC parts catalog.
I had my pump rebuilt a couple of years ago. The techs apparently scrapped the part along with the old hose. I don't know how important it is, but I would like to put it back into the line with a commercial line orifice.
This is the source of air that the vacuum pump is pulling against through the air filter(3) and regulator(1) for the altitude compensation feature on the ME engine pump.
Does anyone know the hole size in that orifice (chock). Could you measure it?
Thanks
PS: I wonder what shape that air filter is in for not having been changed for 25 years???