I might be able to get one for you from a guy who has a stack of model M's. I think they all have the caps/scroll/num lock LEDs so they might not be the right models. I have opened one up and on the chip was (c) 1984, so maybe there was one model with the LEDs that could still switch between XT-AT.
The early part numbers 1390120/1390131 and language variants are XT autosensing capable (1390120 actually shipped with/for XTs, hence the lack of LEDs). The same goes for at least 'some' 1391401 and language variants.
(example of a language variant: 1391406 is a different layout version of 1391401)
The 83-key "Model F" will outlast you and 3+ more generations to come. Take it apart and clean it up - they're well worth the care, especially partnered with a converter so you can use them on more than just vintage boxes.
LEDs don't matter, even the LEDless Model Ms have header on their circuit board for a ribbon cable from where the LEDs go. If the keyboard supports the XT protocol, the keyboard will work but the system will just simply not be able to light them up. Model ##s matter.