1) I know of Hevle Aviation web site that says that they sell them. The price is $12, 500 plus shipping, which probably is not bad at all because it includes a gear reduction hub, so you can swing that big prop.
http://www.hevleaviation.com/Rotec.htm
2) Then there is the 5 & 7 cylinder homebuilt (using VW cylinders & pistons) from HCI Aviation. They sell the plans (I have the 5-cylinder set) and the castings and the complete engine. This engine design has had some problems running on a carb and they said that it needs to be fuel injected to operate properly. It's an "L" head design.
http://www.hciaviation.com/index.shtml
3) Then sometime in the future, there might be remanufactured LeRone rotaries from Le Rhone Engine Works of Auburn. But don't hold your breath, because a new one will probably cost about $100k.
http://www.lerhoneauburn.com
4) Then there are the antique radial engines, if you can find an original one & the parts to make it operable?