I have a team that has been active for a few years and I am unable to find it in CP so that I can add myself to the team. Do I need to add the team to CP? If so, how? Or is there another way to get my team in CP?

Not come across this problem before. Are you averse to giving the name of the team so that I and more to the point, others with more knowledge than I can look into it. As I understand it anyone can form a team and then it should show up.

The one think I can do is see if the team shows up on other projects I run when there is no work from CPDN.

Dave

The team you joined in other projects isn't automatically created in each project you join: BOINC combined - User stats - Dimond | BOINCstats/BAM!.
You might create it here, but as far as I can see none of the other members joined climateprediction.