What are the best locations within the solar system to find Helium 3 excluding the Sun? Where is Helium 3 most abundant after the Sun?
You wouldn't need to travel too far, the moon has been bombarded with large amounts of Helium3.
Where is Helium 3 most abundant after the Sun?
Jupiter, by mass, and Uranus and Neptune, by accessibility. This ignores that getting to and returning from Uranus and Neptune is extremely difficult.
Except for the Sun's core, the helium in the Sun is primordial in the sense that that helium was present when the Sun first formed, and mostly primordial in the sense that most of that helium was created during the Big Bang. The atmospheres of the giant planets are mostly hydrogen and helium -- i.e., mostly primordial.
Saturn's atmosphere is significantly depleted of helium compared to the Sun (and estimates of helium produced in the Big Band), and Jupiter's is slightly depleted in helium. This depletion is thought to be the result of helium somehow precipitating out of those gas giants' atmospheres. The atmospheres of Uranus and Neptune are much closer to primordial.