A few years back, manufacturers were legally obliged to stock
electrical parts for 10 years, mechanical for 7, and cosmetic
for 5 (or was it 3?). What the law currently is, I don't know.

What jurisdiction is that? Is that federal, state (which state)?

Federal.


What if a company goes out of business?

There would be no entity the law could be enforced against.


Do you have a reference?

No, but the head of Sony parts confirmed this seven or eight years ago.