I searched "ISO drafting pens" and had several results, although none from the US or Canada. Wikipedia lists some manufacturers, and here are some online shops from my first couple of pages of results.
I've never used the steel nibbed pens. My grandfather was a draughtsman, and had a complete set, but as I understood it (age 10-ish) they were delicate and needed to be used carefully. I wouldn't buy a complete set on a whim :-)
Wonderful, ISO-128 is exactly it and the wiki explains it perfectly. This seems like a fantastic sizing for pen sets.
The 0.10, 0.13, 0.18, 0.25, 0.35, 0.50, 0.70, 1.0, 1.4, and 2.0 scale with √2. I couldn't tell if other sets were just rounding or dropping the hundredths place. The rotring and staedtler both offer sets in those increments. I suppose this is just common knowledge to those who need it.
The 0.10, 0.13, 0.18, 0.25, 0.35, 0.50, 0.70, 1.0, 1.4, and 2.0 scale with √2. I couldn't tell if other sets were just rounding or dropping the hundredths place. The rotring and staedtler both offer sets in those increments. I suppose this is just common knowledge to those who need it.