Strange indeed. I don't have an answer to your question, but I can quess some explanation.

In the key of G major, chord F#dim is vii° chord, which is very rare in western popular music. That's why you don't see F#dim chord in songs. However, a note F# belongs to Bm (iii chord) and D (V chord) as well. The V chord is used in majority of songs. Therefore note F# should be present in songs which are played in the G major key.

In the standard notation sheet #-mark isn't typically present for all the notes that have a sharp value. The key signature mark in the beginning of notation applies to whole song (or until the key change). Maybe that's why you don't see F# notes in notation?