First, I had to figure out what was meant by "innocent possession." Looking at D.C. cases, it seems to be the possession of a firearm while possessing drugs without a nexus between them. The federal statute dealing with this is 18 USC 924(c)(1)(A), which states in pertinent part
[A]ny person who, during and in relation to any . . . drug trafficking crime . . . for which the person may be prosecuted in a court of the United States, uses or carries a firearm, or who, in furtherance of any such crime, possesses a firearm, shall, in addition to the punishment provided for such . . . drug trafficking crime—The problem is that Virginia Code sec 18.2-308.4(C), which covers the same ground in Virginia, has no nexus requirement.
(i) be sentenced to a term of imprisonment of not less than 5 years
It shall be unlawful for any person to possess, use, or attempt to use any pistol, shotgun, rifle, or other firearm or display such weapon in a threatening manner while committing or attempting to commit the illegal manufacture, sale, distribution, or the possession with the intent to manufacture, sell, or distribute a [drug]. [A]ny person convicted hereunder shall be sentenced to a mandatory minimum term of imprisonment of five years.At one time, the Virginia Court of Appeals had inferred a nexus, but this was rejected by the Virginia Supreme Court in Wright v. Commonwealth, NOV09, VaSC No. 090308. Subsections A & B of this statute contain language that the possession must be "with knowledge and intent", but the General Assembly declined to include that language in subsection C.
So, in my opinion, innocent possession is not going to be a defense in Virginia.