I've spent a couple of evenings looking for 4mm PCB mount banana plugs with specific properties. I've been striking out, so maybe the forum can help. I'm looking for beryllium copper plugs, gold plated, longish and made by a somewhat decent manufacturer. I'd prefer barrel plugs, but other styles are feasible too. The mounting style should be thread, inner thread, rivet or something similar. That's not too critical.
I've been able to find plugs with all the properties minus the gold plating or all the properties minus the beryllium copper or plugs that are too short. I could make do with either of the first two, but I can hardly imagine that specific combination not existing anywhere. However, I'm not finding them.