The admin of CEX.IO has replied to me via email and said they will add DVC/BTC trading when enough people have requested it.

To get DVC/BTC trading on CEX.IO (which is an exchange which has pretty high volume) please complete the following steps:

1.) register for http://cex.io

2.) Go to this link https://support.cex.io/entries/28554767-Convert-NMC-IXC-DVC-to-BTC

3.) Click vote for this feature

4.) You can also submit a support ticket requesting they add DVC/BTC trading asap!