You may learn, as other hobby gardeners have learned, that the florist you consult for advice may himself need certain plant material that you can contract to supply, and perhaps that will be all the work you will care to handle.
When you have decided upon your product and your price, talk to the manager of your local supermarket or variety store; show him your product, attractively packaged and reasonably priced. If you find a market here, do not promise more than you can comfortably deliver, but work out an arrangement whereby you can start slowly and build gradually. Most stores of this type seem to prefer foliage plants, which would be the ideal kinds for your first selling efforts since they are not limited to one season of the year but can be produced and sold the year around.
It would be unwise, at the beginning, to attempt to sell highly seasonal plants for which there is a demand for only a short period each year. That would leave you with a long period of time with little or no return on your investment.