You can use shapeways, imaterialize, 3d hubs or any number of other places.
My advice is that if you are the sort of person that enjoys tinkering with this sort of thing, you are highly likely to enjoy 3d printing also. An Ender3 or similar are pretty cheap these days.
I would offer these for sale on my Tindie store, but as it seems that there are so many subtle variations between different VNAs it's a recipe for complaints.
HexAndFlex