Bonding two boars
is possible, but depending on the ages of the boars it may or may not be successful! Generally I'd say pair him up with either an elderly boar (who may move your current pig down a peg or two, so if the pig you have now is dominant be very careful with an older pig) or with a very young pig, who won't be seen as a threat. Boars are best off in pairs, as three tends to be a crowd with them! Or as you say you can have your boar neutered and pair him up with a sow (or more than one). You may not find very many vets willing to do this here in the UK, and neutering won't change his behaviour but will prevent accidental babies
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If you do decide to neuter, make sure you go with a guinea-savvy vet who is confident in what they're doing, especially with anaesthetic. Also, keep your boar separate from sows for at least 5 weeks after neutering to prevent accidental pregnancies with left over/stored sperm.
It's best to maybe take your little guy to a rescue so that you can meet and greet many pigs with him, which ever you decide. Sometimes they'll do playdays and you can continue the bonding at home if things start well, or sometimes they do longer, residential bonding sessions over a few days. Perhaps keep your current and new pig separate at first, but next to each other so they can smell and see each other. Once they are used to each other, introduce them to each other on neutral ground for a few hours of play time, and once you've done this and they're bonding well try keeping them together in a large, spacious cage with plenty of place to hide away from each other!
I hope you find your boar a perfect pal, and that I've helped you out some
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It might be worth researching some local rescues to you online, or check out Guinea Pig Magazine as they advertise lots of UK rescues
