FWIW, nearly everything RyonaComics sells is conversions by Shinteo. They seem to claim they have Shinteo's permission, but who knows. At any rate, Shinteo's conversions are free after a certain time, so can likely find them easily.
ive seen shinteo tag ryonacomics as a commissioner for models before so maybe that is the case. i can't actually find sindel under shinteo's releases though, i think someone else might have done that one.
Ryonacomics pays shinteo commissions for files. Some of those commissions are kept private so Ryonacomics is the only one with access to them. Sindel is one of those files. There aren't many. Most of Ryonacomics' inventory is available for free on shinteo's Patreon page after a 30 day wait.