It is easy for U. S. citizens to obtain their own permit. Permits are designed for mailing seeds to the States, but usually help get you through customs with modest amounts of permitted seeds that you are carrying with you. Some plants are not allowed entry, especially those listed as “noxious weeds.” It might also be more difficult (and dangerous) to bring seeds of crops of major economic importance in the States. The inspector probably would not let you bring in citrus or corn because of the economic damage that could be done by introduction of a new disease or pest.
Permits can be easily obtained by any citizen by contacting USDA APHIS online: Plant and Plant Products Permits The USDA must first send you a formal application, so allow plenty of time for two exchanges by mail. Permits are good only for the particular port of entry that you specify. E. g. ECHO’s Miami permit will not help me in Los Angeles. To bring living plants, you also need a post-entry quarantine permit and a place (it could be a residence) where the plant will be kept and federally inspected for two years.
ECHO Staff 1992. How Can I Get My Own Seed Import Permit?. ECHO Development Notes no. 37