Are you looking for a plug or socket or both? If you go to the Digikey or Mouser website, you’ll find a huge number of styles that can handle 24 VAC and 0.1 A. Not sure what you mean by ubiquitous 2.5 mm connector. 2.5 mm JST? … not exactly ubiquitous. 2.1 x 5.5 mm connectors are ubiquitous though. Unless it’s critical or going commercial, I wouldn’t be too concerned about 24 VAC at 0.1 A into connector rated 24 VDC at 8 A. Most connectors have an AC as well as DC rating … just have to find it. Line voltage plugs can easily handle 24 VAC, but for safety reasons, do not use standard line voltage plugs for low voltage connections.
Mike