So, the modern barrel ends do fit the old Campagnolo shifters. That's good to know because I was planning to order online but don't want to by incompatible parts.

The shifter cables I have do seem very thin. Several strands actually wore through or broke somehow and I am probably headed towards a broken cable (bad). I want to replace them before that happens.

We don't have any co-ops around here. We barely have any bike shops that aren't sales outlets for ebikes and beach cruisers. Performance is long gone. Bikecology is gone, Ted Ernst is long since gone,... The last brake pads I bought came from Europe (England, IIRC).