There are two methods to obtain Ropalon: the first method is to defeat Rock in Tales of Souls, although the chances of obtaining it this way is low; and the other method is to simply purchase it in the Weapons Shop for 24,800 Gold. However, you need to unlock it first before it'll appear in the Weapons Shop's listing. There are two ways to make it appear in the Shop's listing:
Fight a total of 475 matches.
Clear any of the following stages during Rock's Tales of Souls:
Stage 6 (Ivy)
Stage 7 (Revenant)
Stage 8 (Yun-seong)
Stage 9 (Sophitia)
Soulcalibur IV[]
It can be bought in Character Creation for 7,500 Gold after completing Story Mode with Rock.