ROMABIO has a mineral-based interior/exterior paint.
http://romabio.com/downloads/TDS-EcoDomus-EggShell.pdf
http://romabio.com/products/
I've never used it, but have ordered samples from the company and they are very good to work with, responsive to email and phone, etc. They also have an exterior varnish (intended for decking i think, but you could ask them about use on siding) that I think is the lowest VOC available for polyurethane-type products. That's their manufacturer claim for the varnishes, and I've searched high and low for others (AFM, VT natural coatings, etc) and as far as I know, this claim is true.
