Someone recently asked about cushion replacments for their leather sofa - they received some suggestions. Maybe you can do a search and find the post. It was only in the past few weeks.

Can you list the manufacturer?

Unfortunately it was over 10 years ago so I have no idea

Sometimes there's a tag or info underneath the main part of the couch. Tilt it back to see under. To get the work done, the upholstery places dealing with boats are used to one off custom work. And this is their off season.

This company might help/ Color Options | USA Furniture & Leather (oakonline.com)

Sofa cores are engineered foam done to a manufacturer's specifications, they are not off-the-shelf items you can order on line. That's a common misconception, however - you are not alone. The only correct solution is to get them from the manufacturer of the sofa, and they will be expensive, typically $ 200 per core before shipping. The foam in a sofa is the second most costly component in the build of a sofa, after the cover.

Foam is a low grade material for the seat cushion. It deteriorates progressively over its 10 year life, becoming 'softer' and softer over that time. Pocketed springs and latex are longer lasting. And the comfort level stays the same over its lifetime.

This is a source for cushion foam. A-1 Foam offers the largest selection of quality upholstery fabrics, accessories, and services in the Twin Cities, MN

" A-1 Foam & Upholstery offers a wide range of products and services relating to furniture, marine, automotive, and commercial upholstery. Foam is our specialty. Whether you may need to replace a foam cushion or just need a piece of foam for a project, we can help. We have sewing professionals who are able to sew a wide variety of covers from cushions to pillows, and more. Do you have a sagging cushion on your favorite chair or sofa? Bring in your cushion and we can give it new life. "