Back in the day, when you bought Harpoon in a store, it came with a nice thick manual that was 10 percent game mechanics/90 percent modern naval tactics/strategy. It was a very fun read and applies to any version of Harpoon. I hung on to my copy for as long as i could. Since then ive acquired a nice library of books on the subject that expands my knowledge even more. And since Harpoon is still really centered on NATO vs. Warsaw Pact type conflicts, you can find a lot of books on the subject on Amazon for VERY cheap since they are going to be "used" and sold thru booksellers. I once bought 5 must have books for me for 10 cents and all I had to pay was shipping. Plus if youre looking for things on the web, a good way to find documents on our chosen subject is to do an advanced search and search for only PDF's (search for "naval warfare" and choose to search for only PDF's) there is still a lot of info out there, you just have to dive for it.
But when it comes to scenarios, i took some time a couple years back and downloaded every scenario i could find and ended up with a folder of scenarios thats over 400 files now. And i keep that on a external dfrive to make sure i dont lose it and just point the game to that when i want to find a new game to play. I would make scens on my own but i run exclusively on 64 bit now...but thats a whole other story