Do you already know what breed you want, do you want another Jack Russell? If so I'd start with the breed club, also any facebook pages for owners of/fans of that breed and make a shortlist of suitable breeders, then get onto contacting them, first to quiz them to make sure they really are good breeders (being KC approved is a good starting point but not a guarantee), then if you like the sound of them to find out their mating plans and whether they operate a waiting list.
If you don't know or aren't set on a breed yet there are lots of online quizzes you can do where you input factors like size of dog you want, how much exercise you can offer, any other pets in the home, how much grooming you are prepared to do etc etc and it then generates suggestions. It's difficult right now but if you are prepared to wait until the world re-opens a bit there are events like Discover Dogs where you can meet different breeds of dog including some rarer breeds and chat to breeders and owners?
Obviously whichever breed you go for, you should read up on puppy farms and the warning signs, it seems to have become way more prevalent and horrific than it used to be even 10 years or so ago when I last bought a dog (or perhaps we were all just ignorant and naive back then), smuggling in of dogs from abroad that are often unhealthy and badly bred/raised is also something to be aware of. Obviously you want the breeder to have done and can show you proof of relevant health screening for both parents (not just a vet 'health check' which really only confirms the dog itself is healthy, not its suitability for breeding). A proper health screening includes things like DNA tests for any genetic diseases prevalent in the breed, hip scoring for a breed that has hip issues etc. They should be able to talk you through the reasons for the mating in terms of the characteristics and temperaments of both parents, it really shouldn't be 'we own the stud dog so we use him for all matings' or 'my friend owns the stud' IMO. You want to be able to see pictures/videos of Mum and pups being raised in a home environment, and to be able to visit the puppy at least once with Mum (obviously not atm but in normal times). Look up the signs that a 'stunt bitch' is being used as this is a trick puppy farmers use to fool people into thinking they are just a normal lovely family breeding from their pet dog or similar. Also I am highly highly suspicious of any breeder that happens to have a puppy immediately available when you inquire, especially if the breeder doesn't grill you thoroughly about your home and circumstances or if they give you any kind of 'hard sell', says the puppy will be sold within hours if you don't make your mind up right away etc. They may tell a plausible tale about why they have just this one puppy available right now, and I know occasionally a litter turns out much bigger than expected or a planned buyer backs out last minute or has to return their pup but all the good breeders I have heard of usually have long waiting lists and/or have loads of people contacting them about their dogs who they have 'pre-vetted' for suitability and would have no need or desire to sell a puppy right away over the phone to someone calling up on spec. I would expect to have to wait at least 6 months to get a puppy from a truly responsible breeder, even if they don't operate a formal waiting list they won't do a mating unless they are confident they have homes ready for the litter, of people they already know about/have vetted, and each bitch should have decent gaps between litters (and no more than 2-3 litters total in their lifetime) so waiting is a unfortunate necessity esp for breeds that have small litters, even if you get super lucky and the breeder has a bitch imminently ready for mating and a spot on the waiting list for you, it will take a few weeks for her to come into season and be mated, then the pregnancy time, then pups won't be ready to go until at least 8 weeks, longer for some breeds...
Good luck!