Jens Hansen, NZ
They made the One Ring for the Lord of the Rings movies. They make Movie Ring replicas for fans and can inscribe custom tengwar messages onto their jewelry!
I helped them improve their English auto-transliterator, though it should be noted that a computer program can’t sense context, and won’t be perfect. So, when you select their “Elvish Inscription Checking Service” option, I will be personally transliterating the inscription. You can also send them one of my translation+transliterations, either from the main website or one that you had custom made, and they will inscribe it for you!
If you are looking to getting a set of rings inscribed with tengwar, I can personally recommend you get it done with Jens Hansen!