GiddyUpFlix has lots of gaited horse training DVDs to choose from to rent. I particularly have preferred David Lichman, Larry Whitesell and Brenda Imus. They have some new ones by Jennifer Bauer who trained under Larry Whitesell too.
There plans start at $9+ dollars a month for unlimited monthy rentals. Lots more affordable than buying the DVDs and you can keep them as long as you want. I've really enjoyed their service so far and they have an excellent selection of all kinds of riding DVDs.