Cooling Pipe with Internal Fins

I don't know which sizes or metals, but check Sumitomo.

copper or cuni heat exchanger pipe/tube...

123http://www.copper.org/applications/cuni/app_syscomp.html#Condenser

remove the 123 from above address

Robert

There are companies that produce pipes with what looks a little like a spring that is wound into the bore to increase turbulence.

Anything of this nature will, of course, increase the pressure drop compared to that of smooth pipe.

Which may be important as well <wheeze>.

For the sizes you are seeking you might try boiler tubes with internal fins. They are fairly common.