i left my starter island and build a small base on my second island on which i spotted the merchant, in this map i found 2 star boar roaming nowhere even near a rune, needless to say i quickly caught one and then went back to the same place to find another two star roaming exactly at the same place, i think i lucked out.

we had one on not that far from the starting point on the starter island. just make sure to take the opportunity if you come across one

Them start spawning at 800m away from center map ( i just got lucky of getting one in that limit in my 2nd world) , or as someone said , in boar runestone with 1% chance , in runestones spawns at start 4-9 boars , and if you want to keep respawning you have to kill all boars spawned , if you save one the runestone stop working ( happen to me in same 2nd world where i get 2nd 2* boar but the runestone stop working )

yeah, you can find them, look for those runestones written in red, the one who talks about the boars. you should check it time to time to see if it spawns a 2stars boar

You need to be pretty far from the center of the map for star boars to spawn, but if you saw a one star you're far enough. There's a chance a two star might spawn in the same location.
Find a boar runestone, kill all the boars, and come back in a few days to see what's respawned.