Moments of inertia of planets The three principal moments of inertia of Earth and Moon are reported, for example, in T. J. Ahrens, Global Earth Physics - A handbook of Physical Constants.

I have found reports of the moment of inertia factor $\dfrac{C}{M R^2}$, where $C$ is the polar moment of inertia, $M$ the mass and $R$ the mean radius, for planets of the solar system. 

Are the three principal moments of inertia for the planets of the solar system known?
The planets are very, very close to spherical (the Earth has a variaton of about 0.1% between polar and equatorial radii).  

The rotational inertial for a solid sphere is

$$I=\frac{2}{5}mr^2$$

If you give us details about why you might be interested in looking at the rotational inertia of planets in greater detail, there might be more motivation for putting effort into finding an answer for you.

Just saying.