You have to have a skeleton kill a creeper it is a bit hard but eventually you will get it. I hoped this helps

easy way download this mod http://www.planetminecraft.com/mod/morerecipes-v-13-100/ (look at the pictures) ;D

GET INTO A DUNGEON.

im guessing creepers can drop both gold and green discs...

2 Ways
1 get lucky when finding a dungeon
2 creeper gets shot by skeleton arrow

I found one in a dungeon chest

okay guys think about this...a pit+creeper and skeleton+creepers explode=i die from creeper explosion even IF im outside of the pit

I'll simplify. Skeleton kill creeper = chance of creeper dropping disc (the creeper can't blow up, it has to be killed by a skeleton arrow)

Dungeon Chest = chance of finding disc

Tips: just injure creepers and make sure it is between you and a skeleton. To find dungeons just speed up searching for them by using caves and mining towards any zombie sounds (or cave spiders/skeletons since 1.8)

In my time I have found around 30 - 40 discs with legit methods.

Dungeons aren't something to depend on so keep trying to get a skeleton kill a creeper, and you should get a music disc eventually.