The only other piece of memorabilia that I was directed to because of my recent post (so you don't have to worry about other posts like that; there's not much rare material left to find) was one of those promotional films that were made for U.S. Savings Bonds.
I don't know the story behind this, but around 1980 the Treasury Department decided to promote a new Savings Bond plan by having popular sitcoms do ten-minute films explaining, in character and on the actual sets, why buying Savings Bonds are a great idea. The WKRP one is the only one I've seen. Taxi did one a year later called "Louie, a Patriot," and three years later Cheers did one called "Uncle Sam Malone" (the gang tries to explain to Diane why she should invest in Bonds). These were done as if they were mini-episodes of the series; the showrunners wrote the scripts themselves, and they have opening titles, and some jokes in between the sales pitches. No studio audience, though.
If anyone knows where to find the Taxi or Cheers films, or knows if any other shows did this besides these three, I'd be interested to know. In the meantime, here's the last couple of minutes from the scratchy WKRP one, which offers, yes, an expensive-to-license piece of music ("For the Love of Money" by the O'Jays).