For anyone reading this who is knowledgeable about this topic, where, specifically, can a regular citizen buy personal data about people from data brokers?

https://www.acxiom.com/customer-data/

https://www.epsilon.com/us/products-and-services/data

It's unlikely you can. They're generally only willing to set up corporate deals to sell data in massive bulk. You could buy a domain name, set up a decently real looking website with a corpo looking email, then go to any broker like https://www.acxiom.com/customer-data/ (not affiliated, first one i found on google) and do the whole corporate dance of signing a contract to get what you want.