Your only option may be to search for an RV mattress.

There are many companies that make custom size mattresses. I had one made for an antique daybed. I just gave them the measurements I needed.

Contact ViSpring or Hastens for the very best mattresses out there. Not sure about the 30" width but they probably will do a custom size for you.

Might be good to define your price threshold for top of the line. From a thousand to how many K's?

It's a nearly impossible search with too many variables in materials, construction, etc: )

Is this a daybed? An rv? An antique or handmade bed frame? Would it require a box spring or just a platform?

IMO this size is pretty useless for anoyone but a child so I need more info please . This would be a custom size and very expensive I think.

American Mattress in Eugene, OR makes custom matresses for boats and RVs. I’m sure they could do what you need. They were cost-equivalent to a decent quality standard mattress when we had them do the v-berth on our sailboat, but that was years ago.