Any of the people that sell regulator rigs will have supplies of 10-32 fittings and adapters from Clippard. And a bunch of the rest of us that wanted to do it ourselves and were desperate enough to pay S&H that was 3x the price of a bag of said fittings. Including me.
You'll probably want one of each Clippard part number:
2CPF (1/8M to 10-32F)
11999 (10-32M to 10-32M)
BUT: If you've already mounted your NV-55 via a 10-32 fitting to the regulator, adding a bubble counter to the end of it is a bad idea. Way too much weight on a single 10-32 fitting.
*Edit* - It can be done, but requires a bit more creativity, epoxy, and a sturdier fitting. And a promise to yourself to never bump it.