Hi and welcome!
We recommend to use a good standard rescue whenever possible not only because that is a worthy deed, but also because that is the safest place to get guaranteed quarantined/healthy (i.e. mecically cared for) and correctly sexed/not pregnant guinea pigs from. Sadly that is not an option where you are in the US Midwest,
@happy_piggy - there is no good rescue listed for your state nor anywhere within your wider reach.
Most of the shelters in your state are not ones that provide medical care or that are particularly piggy savvy, but then, neither do most pet shops with adoptables - but where you are, choosing between a shelter and a pet shop adoptable is doing as much as you can in terms of rehoming second-hand guinea pigs, and that is a very laudable aim! Many US shelters have a killing policy if animals can't be found a new home/safe place within a certain space of time, but the animals are often not in the best of nick, so it can be a very expensive and steep learning curve. I know that rescues in other states do their best to pull guinea pigs out of euthanising shelters whenever possible, even across state lines.
Unfortunately that means that it is pretty much a toss up for you where you get your guinea pigs from. Look for piggies that speak to your heart; as you so rightly say, every guinea pig has a right to happiness!
I would strongly recommend to sex any piggies upon arrival, and if you can afford it, please have them vet checked for mites, fungal and respiratory illnesse since you do not have that guarantee from a shop or shelter.
Here is a sexing guide:
Sexing Guinea Pigs: How to Sex a Guinea Pig
Here is our information starter kit for new owners; it does also contain a link to recommended US vets.
" Starter Kit" Of Information Threads For New Owners