Currently I am search for an alternative to “no brainer”, but I always have this issue.
Is there such a thing as a cliche thesaurus?
Not that I know of. If they had one, probably everyone would use it, and we’d just get a new set of cliches and tired phrases. After all, a thesaurus isn’t for finding a different word that has the same meaning simply for “variety”; it’s for finding the correct word when you can only think of a similar one that doesn’t quite fit the connotation you want. (Some of the worst writing I’ve seen comes after a teacher tells a class to “vary” vocabulary, and someone just gets a thesaurus and substitutes words randomly.)
Try using your imagination. With some practice, I’m sure you could come up with a different way to say “no brainer” that’s original and apt.
The traditional solution to this issue is to make up a new phrase yourself. If it catches on, you get your name in the OED.