Manufacturers are only required to supply parts for eight years.

I've heard this many times - 8 years or 10 years or 15 years.
But I've never been able to find any government regulation that
substantiates this general belief.


if there is a buck to be made the manufacturer or other suppliers
will continue to supply these parts.

Absolutely. If I own stock in a corporation which manufacturers
parts for any consumer products, then I'd expect them to continue
to make parts for a particular model for as long as it is profitable
and, obviously, no longer than that. Of course, the implicit monetary
value of customer goodwill must also be considered, especially for
the original manufacturer of that model.