The strip - which is predominantly black with two vertical blue stripes - has been on sale at the club shop for £40 since last summer, but is being replaced because manager Chris Hughton doesn't like it.
Birmingham wore the kit a few times in pre-season friendlies last summer, but since then it has been consigned to the bottom of the players' lockers.
When their kits have clashed, the Blues have instead worn their yellow 'European' shirts.
A club insider confirmed to the Birmingham Mail that the kit is being junked because Hughton is not a fan.
"Some managers like certain kits for all sorts of reasons and the yellow shirts were the design that the manager wanted to use," the source told the paper.
"The yellow kit went down a storm in the Europa League, so the team persisted with it."
That has left fans wanting to share their heroes' garb frustrated: the yellow kit has been almost impossible to get hold of since nobody ever intended it to get regular use.
''These shirts were not manufactured on the same scale as the official home and away kits, so not so many have been available to purchase," the spokesman added.
The paper adds comments from a 'football shirt expert' (no, we're not sure how you earn that title either) by the name of John Devlin, who complains that the idea of including a blue element in the second strip was always a crazy idea.
"My initial thought was that, although it was a smart design, did it really give the club a suitable away option against teams playing in blue?" he said.
"Clubs are losing sight that the purpose of an away kit is to provide an effective alternative colour option should there be a clash.
"If clubs persist in releasing these unnecessary outfits — with ever increasing price tags — I fear a backlash amongst supporters."
The kit has recently been reduced to £30 at the club shop (as have all current replica kits) while Blues bosses are considering plans to offer discounts on the replacement to fans who bought it - though some already believe that the unusual turn of events might make the unloved shirt a cult favourite at St Andrew's.
Manchester United and Arsenal both have third kits that they have worn just once, though neither club puts those on sale.
Liverpool and Chelsea, however, have offended almost as badly by selling their white third strips for £45 despite the players only ever having donned them twice.