This may be a shot in the dark, but I've had a lot of luck using ST...so here goes:

I have a Dura Ace 7800 drive-side crank arm and 53t SG-X B chainring. I'm hoping to complete it by finding a 39t SG-X B chainring, chainring bolts, and (most importantly) a Dura Ace 7800 non-drive side crank arm. Unfortunately I haven't found many people (even on ebay) that have these parts to offer at a reasonable price, if at all. Maybe my luck will change...

The other option I'm considering is finding a Hollowtech 2 compact crankset (i.e. FC-R600, FC-R700, FC-6650G, FC-6750, FC-7950) that has the same non-drive side interface (so I can switch between standard and compact without having two full cranksets). Any condition is fine, though I'm looking to save money on this, so I guess keep that in mind. I will also consider standard full cranksets (vs. compact), but I'm less inclined to go that route.

Thanks and let me know what you guys have!