Is there a good way to increase the chance of spawning Tagami Kazuchi or other random bosses?

No, it's all random.

@MikeDClubb level 8 Rare Enemy PSE boost increases the chances, however increase a less than 1% chance still does not increase the odds very much.

If you manage to get a high level Rare Enemy PSE early on, you can always run through and trigger the next waves/clear them really fast, but the chances are still very low.

I got him to spawn in Super Hard nightfall advance quest alot with +50 risk idk if its just my luck or it's that high idk lol

I tend to run into them often in SH Advanced quests with +50 risks.