Yes indeed! Good to see that folks know of the Orange Songbook.... here is the link also available via the songbook for sources- http://www.geocities.com/CapitolHill/5567/ooooo.html#musI highly recommend Roger Bradley. I have dealt with him for many years now. He also has the two most comprehensive books of songs- on his book pages- see ulster society.
I think it is unfortunate that it is not easier to find recordings of the other culture of the Isle of Ireland. Perhaps the best thing you can do to help make the music more accessible is to give Roger's name and information to your local recording supplier. I hope the orange song book helps.
Many of the songs exist in the DT as I put them there a few years now ago....more to come as time permits. I hope to type in some more this summer.
Conrad