I pretty sure you can buy rifles and shotguns, as long as there legal in CA and take them home that day. I do not believe you can buy handguns though.
You cannot buy them and take them home.... You must buy them and then have the gun transfered by the dealer to your local FFL and have them do all the paperwork and register the firearm in CA and then wait on it for 10 days...
make sure the handgun is on the california approved roster before you buy.
Most of the time.... Its the mag capacity thats the issue.... The gun itself could be legal but the mags that came with it at the time of purchase aren't...... No more than 10 rounds!!
Just about every table at the shows have a sign that says they will not sell to CA residents or even out of state residence in some cases. Maybe if you talk to someone, they might bend the rules but I doubt it. Most gun shops wont sell to CA residents either.