I can't find the Domain Mapping plugin on the list of plugins under "Premium Plugins"

Hi, I got a prob. I'm using both plugins, "Pro Sites" and "Domain Mapping" on my network. What I would like to do is to create a number of levels inside the pro plugin and to enable the "Domain Mapping" plugin only on level 1, not on the first free level..
My problem is that I can't find the Domain Mapping plugin on the list of plugins under "Premium Plugins".
Please help.

Tx