I don't think they are made new anymore. The one I used had been kicking around the workshop since a friend gave it to me 25 years ago. I finally found a use for it :)
I still see them on Ebay, usually as part of some older turbo kits, sometimes just the turbo itself, and they can be overhauled if they are worn.
If you look at other brands of turbos, it should say in the specs if they are fitted with a carbon seal or not for draw through applications.
I have never bought from this site, it's just an example. http://www.lowbugget.com/Schwitzer_Turbo.html