Actualy they are not out of stock. They are available and waiting for Ardupilot developers to implement integration of X2.1 to the code base. Of course Pixracer is another option if you are OK with number of outputs. Last but not least, Pixhawk2.1 is out!
I really do not like Arsov's business model. They design such nice components but are always short in supply and complain why people go for Chinese clones. If they are available why should the store show them as Out of stock?!