init.sls

# mariadb/init.sls
mariadb:
  pkg.installed:
    - pkgs:
      - mariadb-client

include:
  - repos.mariadb

mariadb.sls

# repos/mariadb.sls

# prefixed with "repos." to not have key collisions. maybe
# this is a problem?
repos.mariadb:
  pkgrepo.managed:
    - humanname: MariaDB
    - name: deb http://mirrors.n-ix.net/mariadb/repo/10.0/debian wheezy main
    - dist: wheezy
    - file: /etc/apt/sources.list.d/mariadb.list
    - keyserver: keyserver.ubuntu.com
    - keyid: '0xcbcb082a1bb943db'

server.sls

# mariadb/server.sls
mariadb.server:
  pkg.installed:
    - pkgs:
      - mariadb-server

  service.running:
    - name: mysql
    - enable: True

With the given init.sls, I get:

salt saltmaster state.sls mariadb
saltmaster:
    Data failed to compile:
----------
    No matching sls found for 'mariadb' in env 'base'

However, removing the "include" part, salt tries to set up the package but reports a fail as it has no repo to get it from:

salt saltmaster state.sls mariadb
saltmaster:
----------
          ID: mariadb
    Function: pkg.installed
      Result: False
     Comment: The following packages failed to install/update: mariadb-client.
     Changes: