Indalloy Flux #2 is not the only option for soldering to Nitinol. There is also Indalloy Flux #3.
Both fluxes are strong enough to clean the tenacious oxides off Nitinol, as well as aluminum and stainless steel.
So what are the differences? To start with, it is the consistency of the material. Flux #2 is a liquid flux; Flux #3 is much more viscous and is usually applied by brushing it onto the surface. Flux #2 can also be brushed on, but it can also be sprayed or dispensed.
If you are using a higher temperature solder or have particularly tough oxides, Flux #3 is the right choice.
If your solder contains indium, you will want to choose the Flux #2 because the indium is sensitive to chloride-induced corrosion. However, if you are using a tin-based solder, Flux #3 is an excellent alternative.
Where these two fluxes are the same is that they both require good cleaning and should not be used in electronics applications. Both fluxes MUST be cleaned as soon as possible after reflow. This can be done with warm (not greater than 50°C) water and mechanical scrubbing. If the water is greater than 50°C, you risk additional reactions and possible pitting of the material.
Both of these fluxes are available online at http://buy.solder.com/Medical-Assembly-Materials/C1036_1/ . If you have more questions, check out our medical products page or contact me and I will be glad to help!