I was thinking of doing this last year. Atwood makes the seat swivels for Forest River/Coachmen. I contacted them, and they gave me the some information - including a set of documents for the seat swivel mechanisms.
However, they are intended to be OEM equipment, and they recommended contacting a Forest River dealer for purchase - but if I recall, Atwood would sell them at MSRP.
My main issue I came across was the obstructions behind the seats - namely couches - would make it difficult to swivel the seats, so I shelved the idea as it would take some significant modification of the interior.
You can see here a typical Coachmen/Forest River Class C with swivel seats:
Compared to my Four Winds coach:
I'd have to replace the sofa and reduce the size of the dinette seat to get this to work in my coach... even with the side out extended.
Perhaps other models might not have as many obstructions, so those might be a better candidate for this kind of project.
I can send you the Atwood documentation if you PM me, but what I have are three PDFs, one an installation instruction, and the other two are parts breakdowns. I have no dimensional data.