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If your coach's chair is Flexsteel:
Bauer Upholstery
They reupholster Flexsteel seats. I bet they have a lead on old parts, too.
Used at Bradd and Hall (if they have any)
When you talk with them on the phone, ask about their "universal" pedestal. The way I read the listing, a "universal" would need to be drilled to match the hole pattern that attaches the pedestal to the floor- if it can be drilled, that is. I wouldn't even think about redrilling the
floor to match the pedestal on my coach (structure in the way, and access).
eBay
Visone
You'll have to call them.
Coach Supply Direct
Of the above, I only have personal experience with Bradd and Hall.
A decent welding shop might be able to repair the welded base, if that's what's failed. If it's the parts above that (the swivel) you may have more options for parts replacement.