For whatever reason, sometimes I am only able to find one card of certain players. To be considered a One-Card Wonder, a player must have been active since 1991 (when I started paying attention).
Mike Brumley was drafted by the Red Sox in the second round of the 1983 draft. He had not yet made it to the Majors with Boston when he was traded along with Dennis Eckersley to the Chicago Cubs for Bill Buckner. Brumley made his debut in 1987 with the Cubs and then bounced around for a few years.
In 1991, he finally made it to the Boston Red Sox and played 63 games as a utility infielder. He was not a good hitter. He did return in 1992 to play two more games with Boston before he resumed bouncing around for a couple more years.
This 1992 Score card is the only Major League card of Brumley with the Red Sox. He simply did not play enough with Boston to get cards in any other set. The only reason Score included him was because it was such a large set that it had the space to include part-time utility infielders.
EDIT: I did recently pick up another Mike Brumley card. He no longer qualifies as a one-card wonder.