Hello Marc,
I have never heard from such a program.
The replacement Extractor for the P1900 ,the ordinance model 1920, was build after too many of the flat DWM Extractors were broken.
The "U" shape rear sight was not an armory modification.
It was an allowed modification if the owner/shooter believed to get better hits on the Shooting contests.
The work was done by gunsmiths,sometimes by the owner himself.
Thanks
Stefan