Impossible crank on 1200SL

Hi all Trek riders – I have an old 1200SL and the crank (hope I am using the right word) between the pedals is abandoning me.

the bike shops refuses to change it because the model is old and they claim the crank is no longer to be found.

I tried to extract the crank myself but the standard tools I have cannot take the pedals out, and I cannot recognize the lock ring behind the pedals (pictures attached). Any of you with an example of tools I would need to get the crank out and see the model, so I can find it myself online, maybe?