Diercks and Algyre were three women -- Phyllis Algyre, Eileen Diercks, and Eileen's daughter Ruth P. Diercks, who lived in Iowa.
This ad appeared in the November 1966 issue of The Draft Horse Journal magazine. It shows a team of four Breyer Belgians customized as "four splendid dapple grey Percherons" in "full scotch harness." The wagon was extra.
And this ad was printed in in the May 1967 issue of Draft Horse Journal. It shows a flocked Breyer Belgian in harness, as well as a pair of Breyer Quarter Horse geldings pulling a Prairie Schooner.
I also found some newspaper articles on Diercks and Algyre. This one is just a photo with a caption, from the October 19, 1969 issue of the Waterloo, Iowa Courier-Sun. The caption says that the vehicles were made by Ed V. Ramsey of Waverly, Iowa.
The January 26, 1975 issue of the Waterloo (Iowa) Courier calls the women of Diercks and Algyre "national authorities" on making model horse harnesses.
A nearly full-page article appeared in the January 21, 1976 edition of the Greene (Iowa) Recorder, that provided a wealth of details about the company and its work.
The article gives us some insight into how Diercks & Algyre customized Breyer horses and made harnesses for them. I saved the narrative and the photos in sections to make it easier to read.
A few different companies and individuals have produced flocked Breyer horses over the years. You can read more about flocked model horses in the Model Horse Collectibility blog: