@EspeeGoldenState I'm with you on this one. At the moment all that is out there (Maybe not - as they are from BLMA) are the Leslie S3L-R (which are close) and the Nathan M3R1.
Not sure if Sunrise ever offered the P3's.
Miniatures by Eric offers what looks like a generic 3 chime horn. (His part # NH11) It looks to be a reasonable stand in.
At the moment, I have a bunch of the BLMA S3L-R's for close stand ins. (This may be one item we to settle for - weather we go with the BLMA or MBE)
And - of course, I may have missed some.
Regards,
Wolf