Within the hour, I stumbled upon the cycling shop in Amazon Mexico. I hope it's a new thing, because for years I and others have been carrying stuff down from the US. They have Wheels Mfg. axle sets and cones, tires, rims, spokes, and built wheels with freewheel hubs, Velox rim strips, you name it. I haven't looked for specific group sets yet; I'll do that directly. The last of the decent LBS went modern some years ago. Absolutely anything I have been able to imagine and look up. Some prices are better and some slightly worse, but for that the stuff gets delivered to my door. It's a new dawn for this C&V er.. Like Christmas in December! Easter in April! Independence Day in July! They likely have downtube shifters.
Carry on