Kent only appeared after the Five Year Gap preboot, which was Legion of Super-Heroes volume four (1989 -1994). I believe his first appearance was around LSH v4 #12. He appeared sporadically up until LSH v4 #61, where the series was rebooted. Unfortunately, to my knowledge none of those issues have been collected in TPB form in 15 years (if at all).
I'm actually at a loss for stories that gave him a large role. I can name more arcs where he was absent. He had some good scenes in his first appearance fighting the Persuader in #12 and #13. He put in consistent appearances during the Quiet Darkness, LSH v4 #21-24. Kent had a fairly large part in LSH v4 #51 set on the Quarantine facility. After that adventure, he was deaged by Glorith and sidelined for the rest of the series.
Hopefully that will give you an idea of the timeframe of stories to look through. A great bibliography of Kent's appearances and background can be found here:
Unofficial Kent Shakespeare Biography