They should all have m3d files. If they don't, they'll lock you up just as any missing pylon will lock you up. Don't ask if they were released with this or that, because as I was on the development team of MAW and collected all sorts of odds and ends, and refuse to cooperate with ETO for a number of reasons, I have no idea what a stock install of either might contain. If you have the one m3d, just copy it and change the names until you have as many as you need.
Don't forget that for aircraft with a payload - drop tank, bombs, etc - you don't need a dummy pylon. You can use a real one. Check how I did this for the 109 series. If the loads are wing-mounted, you will need to divide the added weight equally between each wing. I used this system for the Fairey Battle (though may not have released it) and now the AI version flies like a house-brick as it ought to, not like a Spitfire!
To some extent, determining the weight to add is guesswork - you need to cumulate the weight of the crew and their equipment, the fuel allowing for depletion during the flight to the area of operations, and ammunition. In practice, there's a certain amount of trial and error to see, quite simply, what the best compromise is between the AI's "rocket mode" and reasonable laden performance. As you can't fly it yourself to test, it's not as scientific as the development of the flyable flight dynamics. If you do try to fly the AIs, the game engine will add the fuel, etc, anyway, so you'll be carrying it twice...