It would be kinda neat to find out where the "outer space" episodes were made and have a Fraggle pilgramage to see them today.
I wouldn't be surprised if many of them were made in and around the city of Toronto, since that's where Fraggle Rock was produced. Filming "on location" shots local to the studio took place in a lot of TV shows - for example, the kids' TV show ZOOM filmed at Canobie Lake Park in Salem NH (ZOOM was made in Boston, CLP was probably the closest amusement park), You Can't Do That on Television did many on-location shots in the parks and schools near the studio in Ottawa, and I'm sure lots of other TV shows used "local" sites for on-location shots. It just makes good sense for a producer - keep the travel budget down, and you'll have more money to spend on things like Doozer Sticks.
The people to get this information from would be the crew who worked on the show - they're a great source of behind-the-scenes "dirt". For instance, at SlimeCon (a convention for fans of _You Can't Do That on Television_) I happend to spend a lot of time talking to one of the sound engineers who worked on that show, and learned a lot about the production work that went into YCDTOTV. (And, I managed to win a piece of his "private stash" of goodies from the show!)