Local printing companies that have been in business thirty years or more might be a place to start.

It's possible that older clip art has been sold to stock illustration companies. I'd search at iStockPhoto.com which is one of the biggest. On the results page, click only "illustrations" on the left edge to eliminate photos. You could try other companies too.

Another idea is to see if you can find via a Google Images search. If you find it, click it to see a larger version and then click "search by image" to find all occurrences on the web (to find a larger version or a company selling it).