Hi! I am very sorry for your loss. Most piggies mourn deeply when their friend dies, but become a changed piggy when they find a new friend.
There are three ways open to you:
1) You can contact your closest rescues and try to find one where you can take your boar and preferably let him choose a new friend under supervision, as character compatibility is important for a stable relationship.
Here is a list of rescues:
http://www.guineapigrehome.org.uk/gp/centres.asp
2) You can find him a baby boar or one that is as young as possible. The age difference means that they won't hit the hormonal stage at the same time, which should help with keeping the relationship stable. There might be some tiffs when the youngster hits puberty and starts questioning the order of things.
3) You can consider having your boy neutered by the most experienced vet you can find (ask your closest rescues for names) and find him a lady friend. A cross gender relationship is extremely stable because there are no dominance issues and no age considerations, apart from whether your boar is still young enough to have an op and whether you are prepared to risk an operation.
I strongly recommend that you see whether the first way is possible (not all rescue will let you bring your pet with you, sadly). Good luck! I hope you can make your lonely boar happy again!