Special Shapes Inc. was another source for straight brass wire, brass shapes and thin-wall brass tubing, but quite some time ago K&S metals bought them out and discontinued most of the items they carried.

Maybe Albion Alloys (in UK) would have what you are looking for, but with the tariffs debacle I'm not sure if you can buy their stuff and ship it to U.S.
Small Parts Inc. was my go-to source of all sorts of stainless hypodermic tubing and wire, but they absorbed int amazon and I'm not even sure what is still left (whatever inventory is left, it is impossible to search for using amazon search).
Fortunately,
https://componentsupplycompany.com/ carries a good range of what Small Parts did. They even use the same part numbering scheme as Small Parts did. But they carry a small subset of what Small Parts Inc. did.
Fortunately, when all those companies were still around, I've built a decent inventory of their wire and tubing, so I'm all set for a while.