Don't know about Zenith, but when GE quit making sets in Portsmouth VA, they auctioned off the chassis, parts, and even the engineering samples. My Dad (a TV tech/dealer) got most of the parts and engineering stuff. Some rare finds - tubes straight from the factory with big labels on them proclaiming "Not UL type certified - not for finished products" and even some wierd bonded-yoke CRTs that were probably early engineering for the AA/AB/AC chassis, but were never used in production. Flybacks? Dad got 1300 of one type! Sold the lot to the local GE distributor and to PTS Electronics in Bloomington, IN. Resistors, he still has, and as soon as I can help him dig them out, they'll be mine
- something like 80,000 composition and film types. He also got about 5,000 11" long CRT/Aquadag ground wires - who needs them??
I could go on and on, but the point is, I think most is sold at auction, usually to big clearinghouses. When Zenith got out of Mexico, a company in western Florida bought out all of their parts and liquidated them on eBay - I have several SMD/SMT reels of resisistors with Zenith labels and part numbers on them. The company also liquidated AT&T - got a lot of their stuff too.
Cheers