If I'm not too late to add another angle ........
I had no sucess trying to bond two new sows into my herd ( 2 sows + boar) so if you're looking for a new piggie , what about a castrated boar ?
Many Rescues will castrate theor boars to rehome :
You can bond two neutered boars ( as you can bond uncastrated , it doesn;t make boar'noar any different)
If you have a bereaved boy , it is much easier to get him a wife than to make him wait till he's sterile .
A rescue sterile boar is good to go and meet new ladies .
Sows are usually the leaders of the pack . A boar will rumble a bit , try it on and get told to s*d off .
We had S/S/B and S/S (One of the new sows would not tolerate either of the original girls and attached our dopey boar !) But gine with her cagemate . Luckily I had the space to keep 2 groups
Eventually B on his own and S/S living beside him untill the little terror died and I bonded B+ remaining S .
It was nerve wracking but they were fine . She missed her cagemate , he was desperate to be back in a herd
I know with the Rescues ours came from they wouldn't rehome before Christmas unless you were seeking a friend for a bereaved piggie .
Good Luck 