I know Boxrec itself lists amateur highlights and such, but is there an out-and-out database that lists all of their known fights in the same manner? Secondly, any sources for the AMs that you use and rate?
Not that I know of. This sites pretty good for finding out results from past tournaments and championships though. Try typing whatever fighter's name you're researching into the search box. You won't see their records but you will find out some of the tournaments they fought in, who they fought and how they fared in them. http://www.amateur-boxing.strefa.pl/
:good This one has the partial amateur records of some fighters too and there's a Spanish language one which I've forgotten the name of that has a lot of Cuban fighter's partial records too. http://www.boxing-scoop.com/list_boxers.php
Warriorboxing.com is the best source of information for UK amateur boxing. Info regarding domestic championships (i.e. schools, junior, senior novices, ABA elite, CYP's etc) is posted regularly plus some info regarding internationals. There is a database of competing amateur boxers stats (i.e. record, age, weight) that is used for matchmaking purposes but you need to be a club matchmaker or coach to gain access. For international am boxing try AIBA's website and youtube channel.