If there's a second Ryuma for what it matters it's still Zoro. In terms of being "Wano's hero" Luffy is the one to be compared to Ryuma since they both defeated the evil dragon, but because Zoro was no hero at the end of the day. But the only two known characters to have forged a black blade are Ryuma and Mihawk; the only two characters to be confirmed as strongest swordsmen of their era are Ryuma and Mihawk; and the only two characters who dueled their way to the top as their goal are Ryuma and Mihawk. This considered, the only person we know who will forge a black blade (minimum; probably the three of them), who will become the strongest swordsman of his time and whose goal is dueling his way to the top is Zoro.
People need to open their mind a little bit and stop thinking of this manga's comparisons as strict and exclusive, because sometimes it feels like this fandom can't manage more than one thing at once as if that's too hard for their brains. Luffy and Ryuma will be heroes for Wano; Zoro and Ryuma will be top swordsmen in the world who fought their way to the best. No need for any of them to have the monopoly over the guy, that's simplistic thought.