You can find them via Expertflyer using the Timetable option, if you have paid for that, though you need to be careful in that some codeshares are standalone (such as Loganair's service between SOU and NCL) and others have to be combined with another service to produce a valid fare. By using the O and C Routing Codes on ITA Matrix you can rule them in or out. Otherwise if you have something more specific then there are people on here with GDS access and can do searches for you.