No Left Wing: That Bird Flies in Circles!

I was listening to the news today and heard that common label, “right-wing” in reference to a certain “think tank.”  And I got to thinking.
I don’t recall hearing anyone in MSM speak of a “left-wing” anything – as in “left-wing think tank,” or “left-wing lobby group.”  I am not suggesting that these groups do not exist (although I know lots of people that believe the phrase “left-wing think tank” is an oxymoron!) but that these groups are not given the “left” tag as the ones quoting from them or reporting about them come from the same ideological background.
I could be wrong... it was an early morning thought.  But I wonder if this is another example of subtle bias in the media?  Bias by omission.