During the era of flannel baseball uniforms, the undershirt was usually a two-layer wool blend/cotton fabric with sleeves matching the primary team color. A little digging turned up the Canadian mill which made the shirts for the major uniform manufacturers of the day.
Ebbets Field Flannels Fungo Shirt
Stitches Men's Black Chicago White Sox Button-Down Raglan Fashion Jersey
Youth Houston Astros Jeff Bagwell Mitchell & Ness Navy Cooperstown Collection Mesh Batting Practice Jersey
MLB Stitches Apparel, MLB Stitches Gear, Merchandise
Nlcs Houston Astros 2023 Take October T-shirt
Lids Atlanta Braves Stitches Button-Down Raglan Fashion Jersey - Navy
Stitches, Shirts, Stitches Ny Yankees Blue And Grey Vneck Jersey Large
Stitches Men's Brown San Diego Padres Button-Down Raglan Fashion Jersey
Stitches Kids' Youth Navy/orange Houston Astros Team Jersey