Yes, you can get multiple Science Great Leaders, although two is the most that I have had in a game. That appears to be hard-coded in the source code. If you want to increase the probability of a MGL, you have a couple of possibilities. I recommended to Darski that she edit the Heroic Epic to be available with Literature instead of first requiring a victorious army. That works better than Sun Tzu's Art of War, as the Heroic Epic can be built by every player. Darski has done that with some success.You can also set the Military Academy to be available with Military Tradition, rather than requiring a victorious army.
Another option is to change the building requirements, and then set the Heroic Epic and Military Academy to generate leader every certain number of turns. The Military Academy has more justification for that than the Heroic Epic, considering the performance of West Point graduates in the US Civil War and World War Two. The Military Academy gives you the ability to build Armies without leaders in the city that it is located in, and the leaders produced by it, if you set it to produce leaders, have the ability to hurry Wonder construction as a nice side benefit. Just remember that you need 4 cities to support each army.
