LimeWire limits the number of search results it returns. If you search for "divx avi" your LimeWire ultrapeers will stop the search when they have returned a few hundred results. It doesn't mean there aren't more files available but you will have to do a much more specific search to locate them.

There is no limit on the file size, but usually the spam is what you get first because it's much more distributed.

Instead of searching for "divx" or "avi" try searching for "dvdrip avi" or "screener avi" that should take you to the big files.