I agree with
@lauraboara , phoning them can bring light to some options. Websites are not always updated, and also sometimes places can know in advance of upcoming intakes and will be able to say that some of these may become available for you once they have had their health checks and quarantine.
Sometimes though when a piggy becomes depressed it can be necessary to find an alternative. If you do choose a pet shop please ask about the breeder that supplies them, and if you find a local hobby-breeder please be fussy. There are many bad ones, but the good will let you see the parents and all piggies in their care, they will know the personalities of the parents and the babies, you will be able to judge some things by the environment the piggies are kept in, and asking questions on how often they have litters available is one way of gauging if they treat the sows as breeding machines, or if they let them have good breaks in-between. Ask the breeder to get the parents out for you and see how the piggies react when the breeder approaches the cage/hutch, and how calm they are once they have been picked up. Try to get as many clues as possible as to how they treat their pigs, and it's worth asking, casually, how they got into breeding them...
As you know this is a pro-rescue and I already know that you agree very much with that and the reasons why, but for anyone else reading this thread the reasons are because:
a) many pet-shop pigs and private breeders, including those who label themselves as hobby-breeders, over-tax their sows. Labour can be dangerous to sows due to the babies being large and well-developed at birth.
Poor conditions, bad nutrition and back-to-back breeding can increase the risk of birth complications, which are often deadly to both sow and babies. Sadly there really are a shocking amount of commercial and hobby-breeders who simply do not care about the health and well-being of their 'stock'.
b) There are many guinea pigs in rescues and in private re-home sales due to various reasons, one of the most common being that their owners (or the children) have decided that these lovely pets are not for them, and are not prepared to look after them any more. The amount in rescues is staggering.
That said, sometimes (and I have been there) it can work out that at the time you are looking, no suitable piggy partners are available, often due to the boars being already paired up in the rescue, and this can be true of those looking for single sows too. That's not to put anyone else off, it simply works out that way occasionally with the rescues in your immediate area.
Sometimes there are ways around this, involving travel to those further afield, and we on the forum have been known to help each other out in terms of getting guinea pigs to other rescues for dating.
But sometimes purchasing a pig can be the only option if the lone-pig is properly depressed.
@CavySlave23 how is he? and how old is he? Would you mind letting us know where abouts in the UK you are (roughly)
Good for you. Hope you find a great match for your piggie