I’m surprised nobody else has chimed in on this topic. Von Huene’s latest news letter (7/23) appears to say he has new 415hZ Denner Altos in stock. His ‘used’ list includes a Prescott with center tubes for both 440 and 415hZ, and a number of 415 Altos by other makers.
I’ll add that a recent re-voicing they did to my Mollenhauer Alto was exceptional from both a business and auditory standpoint, but I think their reputation has little need for more accolades.
Hope you find what you want!