Check H&Y Electronics in Kentucky. They may still sell them. They are associated with Copper, so hold your nose when you call.
H&Y has the 405 and the 503 but they don't carry the 400v. You'll have to call them because they don't list them anymore but yes they are in stock. I called looking for the 400v but they don't even carry it so I settled on the kl503. The 503 is MOSFET transistor and works great on ssb. One note: the 503 is no longer blue it is silver and made better than the old 503. It has mounting slots now too. It is built like the 400v so you can go by 42's pictures to get a general description but without the fan. It's longer than the 400v which I don't like but it's not that big of a deal.