Great info and ideas, thanks! Good to know that if the rims are still sound then it might well be worth finding a good wheelbuilder to rejuvenate them.

Yes, Laura, you're right! The spoke that broke was on the left side of the wheel. Good call!

When I took a closer look at the rims yesterday to see if I could find any info that would help me date 'em, I realized that they're 28 spoke, front and rear. The old spokes were not double-butted. The rims are "heat treated high strength alloy 6106-T6"---no other info either inside or outside.