I think you are referring to a re-wholesaler.
Our business is slowly turning wholesale for a variety of reasons and my first suggestion would be you need customers to sell to. How do you get them? Reputation.

You need to develop good stock and good relations with your customers no matter who they are.

If you have a million to invests your better then I. We started small, We're talking to local retail nurseries, stopping buy with samples, chatting, asking what they need and how can we save them cash.

One place to sell that you may not have thought about.
Golf Courses. They all have a large budget!

In other words you have to work real hard for it. Most retailers are pretty darn set in their ways and who they buy from.

Good luck to you.

It sounds to me like you want to buy liners wholesale, then grow them on to sell retail??? And yet you title your thread How does one become a wholesaler? That would mean you are selling plants wholesale, not retail. Multiple threads give info on starting a nursery business. Have you read any of those or done some research?

Some liner suppliers will sell direct to you, others prefer you go thru a broker representing them. I'm sure if you let us know specifically what kinds of plants you want to purchase, we could steer you to a source. Or do some google searches on specific plants and their wholesale sources.

By being able to produce enough plants to make it worth someone's time to buy them from you, to be able to produce them as efficiently (cheaper) as all the other wholesalers that are available to those you might sell to, and to have a readily available supply with consistant quality (whether that is high, low, or somewhere in between). That is a tough threshold when you consider the people who are doing it already are so far ahead in all of that than someone who has not done it before.