Someone on another forum has just pointed me to some 'Pulp' figures on the NorthStar website that look perfect and also include 37mm deck-guns, Lew Guns, etc. I'm still interested to see what else might be out there. A 4-inch gun and crew might be fun...
Pulp Figures also has 6 pounder Hochkiss guns as the last pack in the American section.
The Virtual Armchair General has guns of 4 inch and larger under Houston's 25mm ship fittings and guns. There are also some true 25mm (small) crew that would be the same size as those from
Reviresco. Another interesting item from TVAG is the deck mounted Whitehead torpedo tube.