You can find them about anywhere, but best stick to the shipping lanes. If you want specifics, just open the ME. I would rather find them.
RSRD is more historically correct. If you study some books and maps, you can almost always find the large battles.
Most large convoys are invasion forces. Takes some study, but if you know what date they're going to invade a certain island, just search online and get the path. The Java Invasion force is huge.
They get as large as 50 ships and often two groups will come together and you can have 80 or more ships.
Large battles, again just search. Here is one map I use
http://combinedfleet.com/battles/
For earlier invasions, map..
http://upload.wikimedia.org/wikipedi...1-42_-_Map.jpg
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