Hi all, I don't know if this is a stupid request, but I did some research and as far as I know Lilypond don't have the Double Treble Clef neither the alternative percussion clef that both Finale and Sibelius have.
If you guys don't know what I mean, they both can be seen here:
Double Treble Clef: http://en.wikipedia.org/wiki/Clef#Octave_clefs (the middle one)
(I'm not shure if the C clef on the third space is possible because I'm kind of a Lilypond newbie, and I must confess that I never saw one).
I know that the Double Treble Clef is particularly rare, but I already saw a score with it: a Facsimile of French baroque music. As for the alternative percussion clef, actually I think it is a very common one.