By Nigel Duara CalMatters Writer You can talk about guns at California state fairgrounds. You can advertise guns there, too. You can even, in the words of a gun rights group, host “a celebration of America’s gun culture.” What you cannot do, according to a ruling June 11 by a three-judge panel on the 9th U.S. Circuit Court of Appeals, is buy or sell a firearm on property owned by the state. The ruling upholds California’s ban on gun sales o…