Legal Question in Criminal Law in California

Penal Code sections 12020 and 12031 were repealed as of January 1, 2012, which may be why your current lawyer doesn't know about them. (That doesn't mean it is now legal to do what those statutes forbade, though, since other statutes now outlaw much of the same conduct.) But your conviction is subject to the laws that were in effect at the time of the events which led to it. Since you were arrested in 2005, I'll assume that's also when those events took place. Sections 12020 and 12031 were still in effect at the time.

Even when those statutes were still in effect, section 12031(d)(3) contained an exemption only from section 12031(a) and not from section 12020(a)(1). The general rule embodied in section 12031(a) made it a crime to possess a loaded firearm in a vehicle. Subdivision (d)(3) made an exception to that particular rule for licensed private investigators, private security guards, and alarm company operators while acting in the course and scope of their duties.

The statute you say you were convicted under, section 12020(a)(1), made it a crime to manufacture, import, sell, etc. certain types of guns and ammunition. Section 12021(d)(3) did not say licensed security guards, etc., were allowed to do any of those things. It exempted such licensees only from a particular subdivision of the same statute. It did not exempt them from other statutes, or even from other subdivisions of the same statute.

But even if you were right about what the law said, and even if it meant that you should not have been convicted, your conviction would not automatically disappear. You could not "make all record of [it] go away" even if it never should have happened in the first place.

If you're still in prison, on probation, on parole, or otherwise in some form of actual or constructive custody (which might be true even though your question doesn't say so), you could challenge the conviction by petitioning for a writ of habeas corpus. But your challenge could only succeed if the law was on your side. It doesn't seem to be, for the reasons I've already given. There are other obstacles you would have to deal with too, but there's no apparent reason to catalog them here.

I'm sorry I can't be more encouraging.