Youtube is your best friend. :) It'll be the best place to find all, if not, a majority of HeartGold and SoulSilver's sound bits. Other than that, I also nabbed this off of the Pokémon HG/SS Soundtrack Discussion thread. It's where you can download the HG/SS Soundtrack. It's still an active thread currently, so feel free to take part take in the discussion there about the music for the games.
If you may have any further questions, I suggest you use the HG/SS Help Thread, please. Hope this helps you out though, and if anyone has any more suggestions for Symphonic.x.Fantasia please feel free to PM him if desired.