Seiko SK-8 and the Singer are out of production. The leftover with interchangable components is the Newlong Industrial DD-5 (not Newlong Machine Works, they stopped making this machine)
You can find it here
http://www.sewingpartsexpress.com/dd-5/
The machine is about 2500 euros when ordering it.Good machine and the only one available at this moment as the model is old but the Free feed mechanism and the heavy duty aspect makes this excellent for leather but also for connecting layers of belts or making it part of a CNC computer controlled mechanism.
