California Code, Penal Code - PEN § 26525

(a) Section 26500 does not apply to the sale, lease, or transfer of used firearms, other than handguns, at gun shows or events, as specified in Article 1 (commencing with Section 26700) and Article 2 (commencing with Section 26800) of Chapter 2, by a person other than a licensee or dealer, provided the person has a valid federal firearms license and a current certificate of eligibility issued by the Department of Justice, as specified in Section 26710, and provided all the sales, leases, or transfers fully comply with Section 27545. However, the person shall not engage in the sale, lease, or transfer of used firearms other than handguns at more than 12 gun shows or events in any calendar year and shall not sell, lease, or transfer more than 15 used firearms other than handguns at any single gun show or event. In no event shall the person sell more than 75 used firearms other than handguns in any calendar year.

(b) The Department of Justice shall adopt regulations to administer this program and shall recover the full costs of administration from fees assessed applicants.