Crank handke lock mechanism - need the whole dang thing

On the swing arm there is a number 20810on the flat plate where there are two wheel type mechanisms there is a number 90 and a 31 on other side where there are screw holes.
the crank arm has a number 45054 on inside of it.  frustrating in that handyman took apart and trying to make sense of pieces.  Says we need new crank handle but concerned with age we won't be able to find