From what I have seen (and read) there is only a 1% chance that a starred boar will spawn at any spawn point so its going to take quite a bit of time to get a 2 star to spawn.. Each boar stone has up to 8 spawn points but all but one of them spawn a single time. Other spawn points require a 3 day cool down before they will spawn a boar again.

1 and 2 Star boars will not spawn within 500 meters of the standing stones where you display your forsaken trophies. On my main save I have only found 4, 2 star boars total in over 1500 game days and none of them were on an island I had a base set up on. When I found the most recent one I backed away from it and built a quick taming pen before approaching it, lured it to the pen, and built a small farm base with a portal at the pen while the boar tamed.

I lured a no star boar to the pen and tamed it after that and culled down all the no star boars once I had several 2 stars in the pen.

My wife and I are going to try to build cause ways (earthen and wooden) to bridge small gaps between islands and places that we have to sail across we will build a holding pen. Then we will use an abyssal harpoon to move one of the boars. We will wait at the port for a storm. When the storm has passed we will immediately sail it across the gap and continue (so that we won't get caught in an unexpected storm). We have 6 islands to span so this is going to take quite a bit of time. If it doesn't work, I'll just expand the boar farm into a proper base and use it as a portal hub/farming base and breed 2 stars there.