I gave you a link to my TMNT soundtrack w/ SFX, but I guess you didn’t like that.
I don’t think any Nick cartoons have gotten OSTs, aside from The Spongebob Squarepants Movie and its sequel. The show itself makes ample use of Associated Production Music tracks, and you can see a list of all that here (http://spongebob.wikia.com/wiki/Music). It also pulls some tracks from Animation Music Incorporated.
The Fairly Oddparents is scored by Guy Moon, and he has some samples online (http://www.smartsound.com/royalty-free-music/composer/94/) that may or may not have ever been used in the show.
Really though, is there something you’re particularly interested in? Nickelodeon has aired dozens of shows in its many decades of existence, so it’s not practical to desire all the music from all the shows.
Just because it’s a children’s show doesn’t mean you aren’t allowed to appreciate it’s music.
A lot of the stuff in my music library – and the stuff I tend to listen to most – is scores to animated films and TV shows. I think they can have more character than a lot of ""adult" film music.
Glad to help.