I'd recommend doing some web searches for DT and what racks folks put on. I don't own one so can't answer without guessing. It should be easy to find images and accounts of what racks work and what spacers etc are needed to maybe clear the disc calipers etc.
Depending on where you are, you might be able to contact a bike store that sells surlys and ask them too.
You'll find one, I just dont know if stock is low, probably is, but only way to find out is to research and call places.