I have three instrument UTAU at the moment, but right now only a few are available:
Min'yo: Flute
Meiro: Tambourine and melodica (but only tambourine is released at the moment)
Riyoko: Xylophone and ukulele bank (I don't recommend the uke bank, it sounds nothing like an uke lmao but an update is in the works)
You can DL them all at my site
here.