Ludwig did indeed make 26" triple flange rims! My guess is someone pulled the rim off an old set of marching toms. According to the catalog scans under bass trios, there should be 24" and 28" triple flange rims out in the wild as well.
Ludwigfire,
Thanks for posting those catalog pages and resolving the question as to whether Ludwig offered these large, triple-flanged hoops. I played triple timp-toms in my University marching band (12"-14"-16"), and I can't imagine marching with a 26" timp-tom! I'll bet very few were ever ordered.
Mike