Invent your own colour!
The CMYK artwork file should be set up in exactly the same way you would create artwork for a standard print job. The Spot UV file can consist of vector or bitmap graphics as long as the objects to be Spot UV varnished are set in 100% black. (See 'Understanding the difference between Vector & Bitmap Graphics' for more information).
If you are having difficulty setting up your Spot UV artwork files correctly, get in touch and we will be happy to help.