I know Rungvisai was 8th recently thanks to beating Chocalitito but what other Thais have managed to get onto it?
Pongsaklek Wonjongkam was certainly on them for years. Ring Magazine didn't include P4P rankings until 1989. They stopped including them in 2014. I don't know who else you would reference for rankings like that. Maybe Khaosai Galaxy or Veeraphol Sahaprom were on some.
There is the Transnational Boxing Rankings Board that was founded in 2013. They've always had P4P rankings, but I don't think any Thais have been a part of those besides SSR.
I think Khosai Galaxy was ranked by KO. I know they were sort of pushing him hard. I remember in The Ring 80 greatest fighters they had him laughably high. He was above Napoles, Hearns, Ortiz, Gomez, Hopkins, Jones etc;