I want to upgrade my gravel bike from 11 speed to 12 speed but I'm having a real hard time finding a 11-42 HG cassette.

11-42 are a dime a dozen for 11-speed but I can't seem to find that range anywhere for 12-speed?

Is it just me or do they not exist? The closest I found was 11-46.

I could possibly compromise for a 11-40 but I haven't seen any of those either.

There are quite a few actually. I had 11-50 variant of it before and got 11-42 last week for a new build -

https://a.aliexpress.com/_m0c9COa

Great Thanx! 

I just order one.