Has there ever been a left-handed third baseman shortstop or second baseman?
Yes, sort of. I don't know of any who both bat and throw left,
but there are a few who bat left and throw right. Current examples
of left-hand hitting third basemen include Hank Blalock
and Russ Branyan
http://www.baseball-reference.com/b/branyru01.shtml Don Mattingly
played one game in 1986, Mike Squires played one game in 1983