Downstems???

you know, there's these cool downstems, that every hi-end bong has(like illadelph, medicali etc.) they are 18,8mm to 14,4mm(i think) and they aren't that tall on the outside of the bong. It looks like this:
I need one! But I can't find a place to get it. Have you guys ever bought one of these, if you have, please tell me where.

every one does it has bong parts

yeah I couldn't find a i shop that sells these, but I really want one.
I don't live in the US and there are like 2 headshops in my town.
maybe you know a keyword or something that could help me find downstems like this. I don't even know how it's called.