Hey Mr Wizard,
Here's some info that might be useful. If you haven't already, try a Google search on the patent number itself ie, "us patent 4518847". There's a response that links to a company called Crockett & Kelly Inc, here in Colorado. Listing shows them at 640 Compton St, Broomfield, CO (other listings show Erie and Westminster CO, all in the same geographical area). Haven't been able to find a phone number for them, though. The patent looks to be expired, and there's a link to another patent #D281811.
Something else you may want to consider is to use one of the pay patent search sites on the web, plunk down the $$ and do a search that way; may have more information on the company than what's found in a basic Google search.
ETA: Regarding the patent #D281811, there's a company name of Heatech International that's associated with that patent number. Perhaps they were the manufacturer at the time?
The initial search also revealed the inventors of the product, all of them in the local area here, in Boulder CO as well as Northglenn CO. Might also try that avenue as well.
