Umm, actually there is. The max number you can get Genji Shld is 99, just because that's the max you can hold. Don't believe me?

If you trade Thunder Shld in colosseam you win Genji Shld, Thunder Shld is not a contained item, you can steal them, morph monsters into them, find them, etc. So if you really wanted 99 Genji Shlds you could get 99 Genji Shlds, hell you could sell those 99 and get 99 more, there is no limit to how many you can get. These questions only work when the item is contained, I.E. The Force Shld, there is a SPECIFIC number of 3 that you can possibly obtain in the game, no more.