Aqualung has in fact discontinued the "new" Mistral so if you want one, you'll need to see if you can still find one on a dealers shelf.
It was in m opinion pretty poorly conceived with a Titan first stage and a hose connecting it to a cheap looking second stage supporting the double hoses.
As indicated by the poster above, I also fear the lack of success will send the wrong message to the scuba industry. There is a market for a well designed single hose regulator with adequate LP ports that is sold at a reasonable price. The Mistral was odd looking with cheap largely off the shelf parts and was badly over priced - 3 nails in the coffin before it ever hit the water.
One additional factor working against a new double hose reg is the growing number of vintage double hose regs being put back into service. You can buy one fully refurbished and ready to dive for $300-$450 and can sometimes do much better if you find a good example on e-bay, at a rummage sale or in the back room of the LDS. Most of the normally required parts for the more common models and clones of those models are available either new old stock, refurbished, or reproduction form.
That tends to set an upper limit on what a company can demand for a new double hose regulator - even more so now if things like the Phoenix conversion continue to be available where you could have a vintage double hose reg upgraded with modern LP and HP ports for around $550-$600.
On the other hand, as more HP and LP port equipped double hose regs begin to be encountered and as they gain more mainstream acceptance, the demand for them will grow and will eventually outstrip the limited supply. At that point the market will then again offer enough potential to perhaps entice a manufacturer to market a new double hose reg or a suitably upgraded version of a vintage design.