There's no real panic - the 5500 series seem to have many parts in common, so you'll likely find plenty of donor watches with compatible parts.
If you cross reference parts from the 5500 for example http://cgi.julesborel.com/cgi-bin/matcgi2?ref=CIT_5500A and your 5503a http://boley.de/en/caliber/watch-movements/citizen/2198?search_caliber=5503 you can see the similarities. And Borels lists a lot of parts.
The tech drawing is for 5500 to 5503.
If you cross reference parts from the 5500 for example http://cgi.julesborel.com/cgi-bin/matcgi2?ref=CIT_5500A and your 5503a http://boley.de/en/caliber/watch-movements/citizen/2198?search_caliber=5503 you can see the similarities. And Borels lists a lot of parts.
The tech drawing is for 5500 to 5503.