Today at Mincha, the Shaliach tzibbur bowed for each word of Kadosh Kadosh Kadosh, to the left, right, and then center, as we do at the end of Shemoneh Esrei. I have never seen that before. Is there a source for this, and has anyone ever seen it before?
Is there a source? Likely not.
The meaning of Kadosh, Kadosh, Kadosh, following the Targum (as we say in Uva LeZion) is, "HOLY in the Heavens Above, the Abode of His Countenance, HOLY upon the earth, the place where Man serves Him, HOLY forever and ever!" That's up, down, and forever - not right, left & center. (We do tend to bounce upwards with each Kadosh.)
He's likely confusing it with "VeKara zeh el zeh veAmar" - "and this [Angel] calls to this one and says." Since the idea here is that each group of Angels can't say Kedushah without alerting the other groups and saying it in unison, I have seen some bow to the right by the first zeh, to the left by the second zeh, and to the center by veAmar. This is as if to pantomime, "This group on the right, calls out to this group on the left, and they join together in the center to praise G-d."