Sexauer Mfg. carries a complete seat removing tool kit I purchased one from them about 30 years ago.Just purchased one for a friend of mine last year.They are from White Plains ,New York.Check with a local plumbing shop in your area ,they should be able to get you one also.To remove some of the rounded off or damaged seats I have used different sized straight blade screwdrivers.Hard to tell you what seats to carry,you could carry a thousand and sooner or later you run into one you dont have,To get by I have soldered some seats and dressed them with a flat file . 
