> ...but actually getting one has so far proved to be impossible.

Where/when did you try buying? I didn't think it was difficult to get the 1st-gen Phi cards while they were selling them -- especially as it seemed like nobody wanted them. Admittedly I never bought any myself, my employer picked up some 31S1P from a local server OEM for testing when they were massively discounted.

Note that the Knights Landing, the current generation is released socketed only for now, so you'd need to buy a server or the ninja dev platforms Intel sells through Colfax.