Perfect rhymes:
* musto (an archaic word for must)
* costo (a rare word meaning a rib)
Near rhymes:
* busted
* rusted
* trusted
* crusted
* adjusted
* gusted (archaic past participle of "gust")
Eye rhymes:
* also
* hello
* follow
* hollow
The best rhyming word for "gusto" will depend on the context of your poem or song.