Simple

If you take a look in the game interface you'll find all the contain of the mini-map, e.g : ColdMine mark (that small gold mark), it can be changed into another one including for the others.
Same thing in .mpq folder, if you're using Model Editor--->.war3.mpq, and you'll find them there. But if "it's not possible" the other solution is using a mini-map ping (Cinematic - Ping mini-map for player...), so that the player will realize the items location
There are just suggestions