Besides the bell housing and 172 tooth flywheel, the tooth pitch is also different.

I think some of the direct drive starters from other Mopars (industrial, early manual trans slant sixes) would work if the pinion gear is changed out to one with the correct pitch.

Can't find an OEM Hemi starter? The easy solution is to go aftermarket.

http://www.robbmcperformance.com/products/hemi_starter.html