While Rokko Chan itself isn't an official game, you can now get what's essentially the official soundtrack from the album composer, R-MEGA. He has linked the soundtrack from his site, requiring a password to access it (rokko). Although if you like, you can also just download it from us here. The official OST features higher fidelity sound quality than what's found in the game, as well as an unused Dr. Mad stage 1 theme as a bonus.
I've actually been a minor fan of R-MEGA's work for some time, though I didn't realize he was behind the Rokko Chan score right away. While you're visiting, you might want to sample some of his other work, including a couple Mega Man 10 themes done in SNES MMX style, as well as other neat mix-ups.
Top image drawn by Taro