I dug into my photo archive and found pics illustrating those corroded screws. They were in a sorry state but you must take into account that these macro shots always make things look worse than they look to your unaided eyes.
To clean the rust corrosion from those shift levers, I used this Rust remover. It worked quite well. Also used it on screws attaching those TT style elbow rest pads. Those have 'countersunk' heads and I couldn't find replacement, not at the time in 2020.




Head bracket before


Head bracket before


New screws on the head bracket



TT Bar Elbow rest screw - Before


These TT Bar Elbow rest screws (countersunk style heads) I wasn't able to find new ones, I cleaned them a bit and now I smear them with a Permatex Synthetic Grease and wipe off excess.



Rear shift lever before.


Front shift lever before.


Rear shift lever rusty bolt after cleaning


Front shift lever rusty bolt after cleaning