10.5:1 Pistons for '66 273 Block w/ '67 920 Heads

I'm having trouble tracking down a set of 10.5:1 pistons for the 273. I've searched for the last hour and can't find a source. Questions:

1). How do I search the usual suspects (parts houses/fleaBay). What engines will work for what years?
2). Where can I find a set?
3). What will the compression really end up at w/ the close-chamber 920 and a thinner gasket? I understand the volume to be 57cc.

Thanks.