My daughter and some friends are playing Christmas Carols in the local shopping centre before Christmas to raise funds for charity but I am finding it difficult for find some relevant music.

It would be nice if we could find some jazzy or interesting arrangements of traditional carols

That sounds cold! There used to be someone on ebay who would send you parts by email. That might be worth trying. Failing that they could just jazz up the usual ones a bit.

Is playing them straight as four-part arrangements a bit too boring? I think if I was shopping, I might be delighted to hear the usual tunes delivered 'straight' but nicely done rather than murdered in a jazzy fashion!!

def try the ebay digital delivery service.
used it for brass quintet stuff. 2 hours later it was printed off and in booklets. email the seller and ask if he has any jazzed up stuff - they are usually very helpful