fietsbob, I did consider one-piece cranks; my main objection is that their pedal threads are 1/2", not 9/16".

As for the availability of bottom bracket axles, I would like to build a fixed gear, and I'd need an axle that is shorter than what most cranksets require (although, with modern road or mountain bike frame spacing, I suppose a longer bb axle could be used if you rearrange the spacers and redish the wheel to correct the chainline--not practical, though). I suspect that high end Japanese cup-and-cone bottom brackets and parts will always be around, but they can be kinda pricey, and one is unlikely to find them in most shops.