Specific volume of an air parcel
The ideal gas law states
$$ pV = nRT \Leftrightarrow \frac{n}{V} = \frac{p}{RT}\ .$$

For the density $\rho = m/V$ and the mass $m = M\cdot n$ with the molar mass $M$, we get a new formula for the density:
$$ \rho = M\frac{n}{V} = M\frac{p}{RT}$$

With the definition of the specific volume we get
$$ v = \frac{RT}{Mp}\ . $$

So unless you know the molar mass of your parcel of air, you will not get out a numerical value for the specific volume.