Trouble is, if you want to get him a friend of the opposite sex then you will either need to get him neutered or get him a spayed sow. Now a spayed sow will be hard to come by, there is a rescue in Rugby that spay them but don't know where about you are from?
As for getting your boy neutered, well you will need to find a vet experienced in performing this operation on guineas. There is a slight risk with the anesthetic but also risk of the piggie having a prolapse. Many people on here have had many boars done with no problems what so ever but it depends if you are prepared to take the risk with your boy.
I posted on your other topic just now explaining that it is possible for two adult boars to get along & a rescue will help find a pal for your boy. I know you had problems in the past but this could be because the two of them were just not compatible personality wise, it doesn't mean your boy won't get along with another with a different personality.
Good luck with your decsion O0