Schlumpf [Mountain drive, in my case] uses 2 square taper crank arms on them .

neither one have the chainring attached to them .. http://www.cyclemonkey.com/schlumpf-innovations.shtml

http://www.schlumpf.ch/hp/md/md_engl.htm

I got a 54t to go on my Brompton.. the bottom picture shows the unique one for those Bikes .

but You would probably like the looks of the Gippiemme triple I used to make
a 52 -36 double , with a <C> 222 chainguard , on instead of the outer ring being there ..

Its Boxed away somewhere the roadie uses <C> 50,40, 24 race triple instead ..