I have a number of Amperex 152AVP/01 photomultiplier tubes. These are 1/2" diameter x 4" long, end-on tubes that were surplused flight spares from a sounding rocket that flew in the late 1980's. They are bare tubes, but complete with dynode resistor string soldered in place, and wires for HV in and anode signal out. Add a housing, HV supply, and an AC-coupled preamp, and you're in business. I'm not sure what the photocathode response curve is, but S20 is a good guess. I have no way to test these, but they have been stored in darkness in their original shipping tubes, and since there's not much that can go wrong with a phototube, they should be fine. I've certainly used tubes older & more abused than these. The buyer will assume all responsibility and liability for proper HV practice when testing and using these tubes. In other words, you have to know what you're doing- I won't answer any long-distance questions about setup & use. If you don't know a dynode from a photocathode, don't buy one of these, unless it's for the curiosity value.
I'm not sure how to price these. I'd guess that they originally sold for $500-$1500, but their current value is obviously much less. If you have a project that needs phototubes, let me know how many you could use and make an offer.