The Ondestrak

Step 2 Available Contemporary Controllers

Unfortunately, few instruments are available today which mimic the Ondes Martenot's interface. Modern ondes-inspired instruments such as the Ondea, the Therevox Ectro-Theremin, and the Tannerin have all been hand built and are about as difficult to acquire as the Grail. A handful of companies have begun to produce ribbon controllers for digital sound manipulation, such as Doepfer's R2M midi ribbon controller and Analogue Systems' French Connection. Again, price and availability are major limiting factors with these digital newcomers.

EDIT: I've just stumbled across Electric Western's Phantastron, which looks like a very promising, reasonably affordable, all vacumn tube, kit-project instrument that gives a very convincing early synth sound with a ribbon-type controller. All I can say is that it looks very promising.