Liners and Plugs
There are numerous sources for places to find liners and plugs. A liner is simply an unfinished plant that is sold in bulk to a nursery who will upsize the plant into a larger pot. Liners are grown in large amounts and generally are sold fairly cheaply per plant but come in bulk quantities. A plug is pretty much the same thing! Liners and plugs can be found for virtually every plant you can imagine from trees to hostas. When you buy liners and plugs you can provide your customers with patented plants that otherwise you would not be able to produce without a license. Liners can be orders and shipped online and may need some growing time before becoming a sale worthy plant.
Wholesale Plants from Other Nurseries
Talk to local nurseries to see if they offer wholesale plants. You may have to drive a little distance to find good deals but you can then sell the plants at a higher price without having to actually produce the plants. In this case you're acting more as a plant broker than as a grower but you can use this method to supplement the plants you propagate yourself.
Contract Growing with Local Growers
You could also make arrangements with growers in your area to grow certain plants for an agreed upon price. This is a great idea for anyone who may want to expand their inventory but may have space issues in their own production area.
Turn it all around!
You could turn your whole business away from the market side and become a producer of liners, plugs, and plants or become a contract grower for other nursery businesses in your area. There's a lot of flexibility in how to run your business. You just have to figure out where you want to focus!
A personal note: I have not used any of these methods as of yet. I have researched and considered them but for now I prefer to grow my own plants for my nursery business.
More from the Starting a Nursery Business Seriesfrom Growing The Home Garden