I don't even remember what I was Googling for that brought me to The Warp Factor, (EDIT: the spelling of 'Snartemo,' I think) but I followed a link in that post to Gina-B's silkwork blog and discovered a magic keyword: goldwork! There is a needle art out there that uses gold threads. And while they seem to mostly use variously coiled threads, there is one kind called "broad plate" that is just a narrow strip of metal. No. 6 broad plate is 2mm wide, and No. 11 is 1mm wide. Just what I want.
Armed with this knowledge, I've been able to locate Berlin Embroidery, a shop on this side of the Atlantic that carries No. 11 broad plate. Hurrah! The modest cost of a yard of this stuff ($7.50US for 2% gold, $4.50US for 0.5% gold) is well worth not having to Exacto-knife strips of aluminium to an even 1mm.