First of all,
I've been there.
My first kitty, had a very similar issue.
The puking began when she was only about 5, and it was fairly infrequent, so I chalked it up to hairballs, par for the course.
As she got older, it became more frequent. By the time she was 10, it was nearly every day.
The cleanup every day was so frustrating (carpets and puke... yeah, I relate to that).
And I was nearly a wreck knowing she wasn't holding down her meals and getting any nutrition.
I was such an idiot back then.
Took her to the vet multiple times. Ran every test we could think of. The most we could come up with was stomach inflammation.
Slowly, but surely, she wasted away, and I finally helped her cross the bridge.
The vet, being just as confused and frustrated, asked if he could do a necropsy.
I don't mean to be alarming, but what he discovered really surprised me... and explained everything.
She had a tumor, right at a small junction where the bile ducts and intestinal tubes met at the stomach. It slowly grew until it was blocking almost all egress from the stomach. Since it was at the junction, it didn't really show on the scans.
I know it's not the most heartwarming story, but it taught me not to take anything for granted. Keep looking. Expand the search, if necessary. I still wonder, if the scans hadn't been so focused on one area, maybe we would have caught the darn thing earlier.
I'm so sorry you are going through this puking business.
Truly hope you find the solution.