Welcome to the forum
I agree with the others - if his previous owners were trying to keep him with multiple other male piggies then that can explain the fighting.
A baby boy may be an option as he won’t challenge your piggy for dominance.
He absolutely does need a friend for his wellbeing. Even if two piggies don’t get on and can’t share territory, then keeping them side by side in separate cages is better than being kept totally alone - they can interact and have companionship between the bars
Definitely try to find a new friend with the help of a rescue centre if possible, so if the bonding does fail they can take him back and you can try another.
Do note that two boys in the same cage need a cage measuring 180x60cm (which is 70x24 inches) as anything less than that will not be enough space for them and can cause the to fight due to lack of room.
You need to make sure you have two of everything in the cage and that all hides have two exits (any hide with a single exit can be a flash point for one being trapped by the other - even in a successful bond they don’t want to feel cornered)
If they don’t get on and if you can’t return the second piggy, they will have to live in separate but side by side cages. Although you say a ‘back up small cage’, the measurements of it are essential - In the case of side by side living you must make sure both cages measure at least 120x60cm (48x24 inches minimum), as anything less than that contravenes cage size and welfare requirements and cannot be used at all, not even for a single piggy.
Bonding is a specific process done on neutral territory. You can’t just put a new pig in the cage of your current piggy as it will be seen as a territory invasion and will cause a fight.
The bonding guide below explains the exact process. Do remember that successful bonding comes down to the two pigs being character compatible
Bonding and Interaction: Illustrated Bonding Dynamics and Behaviours
A Comprehensive Guide to Guinea Pig Boars