your best bet is simply going to the website of that player’s college team.
thebaseballcube.com is good too though, just a little hit-n-miss sometimes.

For HS stats? Good luck. Few people, outside of the coaches for the HS, keep ‘em and no one bothers publishing ’em and the stats don’t matter from a draft perspective anyway (with the possible exception of noting if a player broke an important record in his state or something).
Just don’t worry about including ‘em in your writeup. They aren’t evidence of anything.