Muggsy was the nickname for 13 year old Margaret Malloy. Muggsy lived with her older brother, Nick, a cab driver, in a furnished truck parked behind Gus's gas station. The show followed Muggsy life in the inner-city and the various problems she faced growing up.
Unlike most of the other Saturday morning shows, there weren't any elements of science fiction, fantasy, or horror in Muggsy. Instead, it dealt with contemporary issues (drugs, violence, gangs, etc...) of the time. Only 12 of the 13 episodes aired.
Like most non-Krofft and Filmation series, Muggsy did not have much a life in syndication - at least not in the US. The show was aired four times in Germany from 1981 to 1985. To my knowledge, no episodes of the series are circulating among collectors/traders. If anyone has access to any episodes (even the German versions!), please contact me.
The Museum of Television and Radio, located in New York and Los Angeles, has several episodes of the series in their collection. For more info on how to find this and other old Saturday morning shows, check out this page