casaschi

They are available, the issue is the amount of space required. For positions up to 5 men you'll need about 7GB. For the 6 men tablebase you'll need space in...

The garbochess.js engine supports underpromotion, see for instance this implementation with a different user interface: http://pgn4web.casaschi.net/engine.html?fs=5r2/6Pk/7p/2pB4/8/q7/8/6RK%20w%20-%20- I can't comment on the original garbochess web interface though.