Is this the model you have?
https://www.rolleiclub.com/thedarkroom/?p=3084 This is the Model 1 Automat 1937-39, there is a type 1 (serial nos. 568516 - 610645 and a type 2 (serial nos. 610646 - 804999). As far as I know they both use the same finder hood. Post war Automats have a different finder but it might also fit.
I have never seen a repair manual for this model so have no idea of any part number, but I doubt there are any stockists of parts for an 80+ year old camera. You could try various repair people to see if they could help, check ebay or look for a suitable 'parts' camera (won't be cheap).
Somebody on Photrio may have some parts lying around.