I'll be blunt:
Write them yourself. Karaoke effects is (almost) all about showing off your skills, if you're just using someone else's effect you're missing the entire point of having an advanced effect. If you want to learn, there's several examples already included with Aegisub. It's rare for people to publish their effect scripts.
The other (much more common, I think?) option is to use one of methods that don't involve direct scripting. You could for example
use simple-k-replacer,
line-per-syllable or
multi-template. And you'll find many good tips on making karaoke in
the karaoke help thread.
Though if you insist on seeing some full-fledged complete scripts,
here are some more examples.
And there is of course also other software for generating karaoke effects.