Bulbs as in flower bulbs?
You will probably need a license from your state's Department of Agriculture -- it would probably fall under the category of horticultural production of ornamental crops, and would be called a nurseryman's license or something along those lines. At least, that is what it is called in Michigan.
You will need that to allow you to legally
sell both in-state and across state borders. With the license comes an annual inspection, and the inspection report generates the phytosanitary certification that you need to accompany interstate shipments. That is the form you've probably seen on packages of nursery stock coming through the mail that says something to the effect of "This nursery stock has been inspected by the X Department of Agriculture and appears to be free of pathogens and insect pests, yada yada yada....."
Something along those lines. Try searching online at your state's Ag. Dept. website.
There could possibly be some Federal permits if you want to trade in any endangered species.