Check if he has gone to Sen Temple area

found him there but he  is not selling anything to me

I didnt find anything here? because I miss it too. I killed him in cold blood when he decided to not sell my anything 

General tips: don’t get greedy. Slowly chip away his Hp before you go for parry. Firecracker can help.

Phase 1: Bait Isshin to do dash and cross slash attack. Dodge/run away from it and then attack him one or twice. Slowly chip away his health. Once his health is reduced to acceptable level, you can start to parry him to kill him.

Phase 2: Be ready to run around (but don’t jump off the cliff). Bait his jump attack. Dodged to side and you should get one or two hits. Once comfortable you can try to parry his sword and spear combo that ends with a thrust. Mikiri Counter it. Isshin hits like a truck and very aggressive. Unless you are very confident with your parry skills, be patience and hit once or twice will do. Don’t forget to guard against his firearms.

Phase 3: same as 2 but this time he has lightning attacks. Be ready to jump and lightning reverse it. Will get a few free hits and posture damage. But careful, if you failed the reversal he will kill you very quickly.

Sword saint is a very fun boss. He will test your patience and very exciting to fight. Ironically I had more trouble with Genichirou. Can’t quite get the dodge timing of his mortal draw down. Always wasted two or more gourd there.

Older Isshin is harder for me. Those fire attacks are crazy.