There is a sticky "MPC 60 FAQ / MPC 60 BIBLE / Please Contribute" on the top of this forum...
http://www.mpc-forums.com/viewtopic.php?t=29188
The answer is in there. It use Double Sided, Double Density disks DS/DD. The disks has only one hole and is 720kb. You can get them here:
http://meritline.stores.yahoo.net/dd-fl ... ellow.html
http://meritline.stores.yahoo.net/dd-fl ... k-red.html
Some people use newer disks (1,4mb) with tape over the one hole to trick the floppydrive. Some users says this is a bad thing to do since the disks are made different, and the result may be that you loose all your data over some time.
This topic is also covered on this SP1200 FAQ site: (which is great!)
http://members.iinet.net.au/~jake2/base/love/faq.html