There is a free sample Tutorial by Tony McManus which is a good intro. And I see at the same site there is a how to play Donal Og tutorial.
However I also see there is a video on YouTube of someone playing Donal Og (Tony McManus cover) which I would guess is the same. But it is not in DADGAD it looks to me as dropped D.

So if it is just for that tune it might not be necessary. But if it is more general then indeed get a few chords off the net and then have an experiment.

Or his a third option. Get a spider capo or partial capo so that you just have the second fret covered on the third, fourth and fifth strings and you will have a set up that sounds like DADGAD but can play the chords you already know...