There’s no new source for them but for used all 89-90 Cougar LSs came standard with the digital dash, so if you can find a bezel from one there’s a good chance the buttons will come with it, like this one in this listing
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However, the functions those buttons access will not work anyway on your car. The digital dash uses fuel flow data from the PCM to calculate the various average MPG and distance to empty functions in it, many older OBD 1 PCMs had that pin active but not the 96+ 104 pin EEC V PCMs, the only ones that did have that hardware were the ones used in Mark VIIIs, Explorers with the info center, Town cars and CV/GMs with the digital dash option. Nothing that would readily swap into a 3.8 Tbird