Billiken has officially announced their Real Model Kit Series Sanda Vs. Gaira Set. These unpainted and unassembled vinyl kits stand 31/30cm tall once assembled (Sanda/Gaira), and the set retails for 15,400 yen. It can be pre-ordered now from Billiken with release scheduled for May-July 2021.
Since Billiken has announced their online shop they have released a few more kits, their latest announcement is Frankenstein's Monsters Sanda Vs. Gaira kits. Both will stand 30cm tall (perfect to match X-Plus 30cm figures), and are unpainted, unassembled kits, designed by Masao Fukuda which will be released spring 2021. Of note these kits sell out fast so if interested is is wise to keep an eye on there site here for there release.