Hi childlost,
In addition to Foam Order, some of the manufacturers listed in post #21 here could also make a custom size for you (you would need to call them to confirm which ones) and there may also be some local manufacturers that can make custom sizes (mattress or foundation) as well.
If you let me know your city or zip I’d be happy to let you know of any I’m aware of that are close to you.
In most cases they would charge you for the next larger size up.
Phoenix