I transcribe everything by ear, which is the oldschool approach to it.
Some DAWs have built in audio to MIDI converters, and some pitch correction VSTs like Melodyne also have the ability. Those usually aren't perfect and really only work if you can isolate the parts you need transcribed.
Then of course finding a transcription that someone already did(like all the tracks on vgmusic) is a possibility if that particular theme you want exists there.
Only other thing you can do is hire someone to do it for you(or hope you find someone willing to just do it for free).
If you can hear a note and then play it on your preferred instrument, or just know what the pitch is without a comparison tool, you have all you need to transcribe it yourself. That's largely what the process is... repeatedly listening to the audio and picking the parts out you want and putting the notes down into a DAW or notation editor.
I recommend just trying it yourself, it is pretty fun once you get going. Kind of like putting a puzzle together...