Yup, 29.8 dia. seat posts exist, just not in Peru.
There are couple of tasty looking posts on that site julk. Your NITTO S84 looks nice as does the Tange CrMo Seat post, they're a bit heavy though.
I don't think there's much chance of my Nomad Mk.1 frame breaking IanW, the thing is built like a tank! That frame set has been through a lot that it shouldn't have survived. And as far as saddles, I'm on my third Brooks in four years so that's not really a worry.
Thanks for your input. I emailed Andy Blance so we'll see what he has to say.