A healthy guinea pig does not have any dried mucus. Sounds like a URI. Most petstore guinea pigs also have mites, which you will have to pay to buy Ivermectin and to treat the pig(s) for. Guinea pigs are social animals and need to live in pairs, threesomes, etc.
Where I got my piggies:
Precious- Free on Craigslist, person moving and didn't kids want her any more
Sweetheart and Cutiepie- Free on Craigslist, person too busy with college
Rosie- Free on Craigslist, "kids didn't want any more", really was that she had major health issuses that we resolved after adoption. Some are ongoing.
And I adopted my dog from the Humane Society.
"Don't breed or buy while shelter animals die" is the motto around here. When you buy a guinea pig (or any animal) from a petstore or breeder, you just make more room in the petstore for another animal, and more room at the mill for more animals. You also then create a demand, telling the breeders and mills to keep breeding because people will buy the animals and put money in their pockets. There is no such thing as a reputable breeder. No animal should be bred when there are millions of homeless animals. I volunteer at my Humane Society and although we do as best as we can, we still euthanize 1/2 of the animals that come in. No animal should ever be euthanized without a necessary reason, not because there are just too many animals on this planet. It is for this very reason that I only adopt animals, I do not bring more animals into this world when there are already not anywhere enough homes for the ones that are already living.
If you don't have a guinea pig rescue near you, then Craigslist is the next best thing. With Craigslist you have to be careful though, because breeders frequently post animals on there. Most cities have their own Craigslist's, so you wouldn't have to travel far to get them.
Here are guinea pig specific rescues:
https://www.guinealynx.info/rescue_organizations.html
but many dog/cat humane societies and shelters also take in guinea pigs. Here is a list of guinea pig vets.
https://www.guinealynx.info/vetlist.html They are hard to come by, mine is 1 hour away from me, while my dog's vet is 5 minutes away.