Although some people may class this as cheating because of the name, in fact, it is completely the opposite! You can get full stats on strength, defense, magic, dexterity, and vitality without even cheating, but it can take awhile to do.
Before we begin you need to acquire the Morph Command Materia from the Temple of the Ancients in disc 1 (please note this is missable!).
Let's Get Powerful!
This one can be tricky depending on who you go and Morph, but the best place to gain Power, Magic, and Guard Sources is in the Sunken Gelnika. However there are other monsters which you can Morph into different sources.
Now that you have the Morph command materia, you should also have Yuffie (one of her very few uses in the game) since her final weapon does not become weak when trying to morph something. Once you have that you can fight the following enemies for certain sources (please note that only the best results are listed but you can find other places), instead of killing them normally, the killing blow must be with the Morph command.