Try here; check for region 1:
https://www.buydvdseries.com/product-TURN-Season-4-DVD-Box-Set-4541.html
And try here, if you have a region free Blu-ray player
the complete series:
Appreciate the info WH. I already have 1-3 DVD. Something strange about the link for the single DVD. Picture is of wrong series and the description talks about season 4 in the future. I could not find that a season 4 DVD was ever made as a single.