if youre still trying to figure it out im pretty sure if you establish taggeco on the planets you can put it on youll get him, though i believe some other factions can also get him

Ulric Tagge and his Tagge BCs are unique in that the CSA, Imperial Warlord factions and the Empire proper are all in the running to get him. For reference, Imperials can get Ulric Tagge as a Tier 2 Legitimacy option and doing so will lock the CSA from getting him and vice versa. Legitimacy unlocks are RNG though, so as the CSA you either have a lot of time or no time at all to make your own play for him.

As the CSA you need to build Tagge Co and then hire him through the political menu. Planets Tagge Co is available to be built on are listed in the influence info window, the button with the heart shaped icon on it. You will need to scroll down a bit to find it.

Depending on GC and starting era this may be easier or more difficult than you would like. For example starting in Known Galaxy Era 7 you can get him near instantly as you start with Bonadan. However if you're starting in era 1 you have to push south to Lantillies near Hapan Space.