ive been getting into these magnetic holders, for your nrl cards you need size 35pt, its about standard for afl, crucket, nrl and others. it goes up from there, the bigger the number the thicker the card you can put into it. i use 100pt and 135pt for my really thick nba and non sport patch cards. i also buy the stands. i get all mine off ebay, both holders and stands. heres a pic of the stands in action
http://i698.photobucket.com/albums/vv348/BLOWN_8/AFL REDEMPTIONS/cardshelf.jpg you can see all the cards have those stands and the MJ is in a magnetic holder like the ones your talking about! hope that helps mate