As with every provider, the Parallels provider has a custom box format.
The actual list of official boxes provided by Parallels is available on wiki page.
You can also look up all community Vagrant boxes for "parallels" provider and find the box matching your use case: https://app.vagrantup.com/boxes/search?provider=parallels
Adding a box from the catalog is very easy:
$ vagrant box add parallels/ubuntu-14.04 ...
You can also quickly initialize a Vagrant environment with the command:
$ vagrant init parallels/ubuntu-14.04 ...