Check out Psalms 23 on my player that I wrote. My buddy played violin and his wife played cello. There are lots of good songs with violins in them. My mind just went blank though, lol. I can't think of anything. I think it's the medication...:^(
Ha.. at first glance I thought this said "worship with violence" I was like.. wohhh... But, it's not. Personally I LOVE when we get the violin to play with our team. I think "Oh Holy Night" would sound awesome with the violin.
I suppose it all depends on what the violin player or players is comfortable with. Are you having a string section or a single player? Can he/she/they improvise and at least follow a melody by ear or do they need sheet music? Can they add their instrument(s) to fit what's being played or does everything have to be exactly like on the recording? Are you willing to add an instrumental section to fit the violins in?
I'm a sax player and wouldn't be doing much of anything if I needed sheet music or if everything had to be like the recording. There are times that we'll add sections to the recorded song just to have instruments playing. That being said, Third Day has versions of many traditional Charistmas Carols done in their style that have violins playing in the background. "The First Noel" and "Angels We Have Heard On High" are 2 that easily come to mind as we're doing them this week and I just was just listening to them.
Song suggestion: Here I am to Worship by Tim Hughes
The verse words fit very well to many of the Christmas themes (think John 1)
Works very well for guitar and violin, since I've done it with my wife like this. Either the violin player improvises an alto line in the verse, or you write one for them. The violin can then go high in the chorus. (I don't know of any recording like this, and we don't exactly have an arrangement written down, but just improvise it).
You could do even more with two violins, and having a cello to play the bass would be cooler yet!
To tag on, there's a live version of Offering by Baloche I saw a video of and they incorporated a cello so you might be able to do something similar with the violin instead. It sounded amazing and I couldn't imagine why the violin wouldn't either.
I see below Michael Letus has offered excellent advice. I might add that compared to the time and trouble of locating violin parts that may or may not exist, you can create your own (or the violinist can) that may be just as good as those found on recordings.
If you know how to write down music, you can listen to something you like -- even an "obbligatto" for some other instrument that would seem to fit the violin's character -- and, listening over and over and over and over, learn it well enough to write it.
Or you can ask the violinst to listen over and over and over and over -- the way many guitarists learn to emulate those great players on the CD's.
You could get adventurous and try making your own part -- learning how to improvise is one of the great useful skills that ANY musician should learn, for a richer life, for ability to give depth to music. Learning how to make up music - to let the soul speak - is just as important as learning how to read notes, or copy something one has heard. We chat all day, making up words in the English language, not giving a thought to the fact that we are "improvising" this conversation. So why not start speaking out spontaneously in Music Language?
We don't start because our first efforts sound (and are) immature, the babbling of babies. So we just keep doing it and listening and thinking and before we know it, we can improvise. Music Language is way easier than the English Language. The only hindrance is fear. So fear not!