I'm not aware of any genuine FSX Yak-3. But I do have the Captain Sim FS9 version, however never tried it in FSX.
When it was released ages ago it was a absolutely stunning model. After all these years it is still a great model.
The Mikoyan-Gurevich MiG-3 was actually a completely different aircraft than the Yakovlev Yak-3. The Mig-3 was one of the first Russian modern fighters (although not really a huge success) and was used in reasonable large numbers in 1941. The Yak-3 was a development from the Yak-9 (Yes really! This is not a typo), and entered service in 1944.
The Yak-3 can be regarded as the Russian wooden wonder as to save rare materials a lot of plywood was applied in the construction of these aircraft.
Sorry the screenshot is taken in FS2004, but as you can see still a great model, with a lovely VC.
Cheers,
Huub