Sorry for the late reply, but I literally, just now made a bandcamp account! You're pretty much the first one to know.
This game contains 3 original pieces of music that were made specifically for it. They are now available as a mini-soundtrack on said brand new bandcamp account here: https://cyberscherzo.bandcamp.com/album/pretty-otaku-thunder-dragon
You'd know them as the Title Screen music; Isabel's Apartment music, and the Sex Scene music.
The rest of the tracks are from various royalty free music libraries; thier composers are all listed in the credits and readme, but if there is a specific track you wanted to find I can point you to it. Some of them have specific ToS rules that prevent me from reposting the track or direct linking to the file; but the websites for most of the other music sources are:
http://d-symphony.com (Sushi Restaurant BGM)
https://maoudamashii.jokersounds.com (Comic Shop BGM)
http://www.tam-music.com/ (The Music when you first meet Isabel)
https://incompetech.com/music/royalty-free/music.html (The intro text chat)
http://www.rpgmakerweb.com/a/visualnovelmaker-music-sound/modern-day-music-mega-... (the 'city' BGM: Side note I have a version of this that allows non RPG maker use)