I believe some parts from 7546 & 7548 movements are interchangeable with the 7549. Same thing with the 6309 for mechanical parts. I've also read of a replacement with a 7c46 movement but the stem needs to be extended.
Here is the parts reference:
http://service.seiko.com.au/pls/sei...,P21_CASE_NO,P21_ITEM_CODE:7549,7009,S60583J1
Here is the parts reference:
http://service.seiko.com.au/pls/sei...,P21_CASE_NO,P21_ITEM_CODE:7549,7009,S60583J1