I have met a lot of people who before meditating say the same thing - that they don't have an internal dialogue. The first step in meditating is to observe, and gradually become more aware of it.
For the past 6 years I have been using one simple technique to keep your mind focused.
Count in your head
"one"
breath in
(while focusing on the sensation on the tip of your nose)
breath out
(focusing on the same/different sensation)
"two"
*repeat until 10, and start at 1*
If your mind wanders, return to 1.
Sit down and do this for half-an-hour. Any time you scratch, or move, or think, or get bored this is your internal dialogue.