The cure for RAD-X is only in After the Flash 2: Osaka and its name is OH-108.
It is found in the Medical Bunker in Osaka, Japan and is a cure to RAD-X Made just before the flash.
For all lore reasons this cure for the virus is STRICTLY forbidden in every game but After the Flash 2: Osaka
Its Appearance is a needle filled with a gold-yellow liquid.
This can also be found in the After the Flash 2 Remaster by the Project Spark team.