1 1st MO Disk - Tiger puzzle
The first MO disk can be obtained after you solve the tiger room puzzle by inserting the right gemstone. The room is in the west wing of the mansion 1F. Note that you will need to get the helmet key first.
2 2nd MO Disk - Lab B2
The second MO disk can be found later in the game in the lab B2 floor. You will find it on a table at the end of the corridor in B2.
3 3nd MO Disk - Lab B2
The third MO disk is in B2 as well. It's in the room right next to the table where you found the 2nd disk. You need to unlock that room first by solving the computer room puzzle in B3 and entering the right passwords.
4 1st Mo disk reader - Lab b3
The 1st Mo disk reader is located on the B3 floor of the lab. This room can be accessed through the ventilation hole of the next room as its door is locked.
5 2nd Mo disk reader - Power area
The Mo disk reader is in the reddish room next to the power room area. Go to that area prepared because there are lots of monsters in the corridors.
6 3rd Mo disk reader - refueling room
The 3rd Mo disk reader is in the room where you refueled the small fuel capsule.
7 Any Mo Disk fits anywhere
Any MO Disk fits into any MO disk reader. It won't matter which disk you insert in which reader, so no specific order is required.