Check eBay, and search for "sachs". I just did, but could not find any currently available. They are somewhat rare, and thus generally go for over $100 US.
Yes, Atkins Rotary custom builds single rotor engines from Mazda parts. Their site seems to be in the process of being updated right now, but suffice it to say that if you have to ask the price, you don't want to buy it. They are very impressive engines though. I have seen a Dixie Chopper single rotor lawnmower run 38 MPH and pull wheelies.