Sourcing a 20mm wide espag rail

[Lower]

Anyone know where i can find one of these or if a 20mm groove can be adapted for a modern 16mm wide rail?

The old rail was so rusted that its virtually disappeared but the window itself is still in good condition. I don't really want to replace the window as the adjacent windows won't match so does anyone have any suggestions as to where i could find a replacement or adapt something to make to fit?

Old rail was made by SI.

 

[crank39]

I think you'll do very well to find a 20mm espag rod now, most will be about 20yrs old so a strong chance thet they're obselete now, most stuff as you'll know now is 16mm, made to fit the standardized 16mm 'euro groove'