When you have bought all the packs available using the first pack glitch, you should be left with one set with one pack left and one set with a bunch of packs left. Well you can use this glitch to buy those two sets for only 300 DP.

1. Highlight the set with one pack and push L.
2. Highlight the other set and push L.
3. Open that same set and deselect one of the packs.
4. Highlight the set with one pack and press R.
5. Highlight the other set and push L.
6. Highlight the set with one pack once more and push L.

If you did it correctly you should be able to purchase all the packs for 300 DP.