I don't even care that they're supposed to be rare in universe.
Nice part about defining your own alternate timeline is that you don't have to follow the official version... In my universe, Earthwerks FWL has been churning out Fleas since they captured Asuncion and Bernardo somewhere in the 29th century. These are the only two facilities that build the Flea, so they are mainly seen in Marik space, filling the position in lances normally reserved for the Locust (The FWL does not build the Locust). Even though Asuncion has seesawed between Marik and Liao, attrition has reduced the Capellan Confederation's supply of Fleas down to no greater than would be expected of any design being salvage across the border. What all this means is that Marik will have a bunch of Fleas (I think it is something like 15% of all light Mechs should be Fleas), Liao and Steiner will have a few (Maybe 1/2% - 1%) and Davion and Kurita will have only the rare example.
In the end, I think I'll probably treat the original Flea as just that, the original, and if the Flea gets a "Classic" face-lift, say that all Fleas after a certain year were built with this look. That means that when Wolf's Dragoons shows up with their stockpile of original looking Fleas, it will just lend credence to the idea that they raider a Star League supply cache... And I can still have a home for all while old ones, while it explains away the new ones.
Caz