How can I build up stamina mainly in my arms as I am a drummer and playing fast songs for half an hour is very tiring what would be the best exercise to do?

Do sports. Stamina can't be just 'arms' or 'legs.' Stamina is how fast you get tired/weakened from doing actions that get your heart pumping faster. What you gotta do is just practice more with exercises that drain your energy. That way, the hurt will get more 'used' to those actions and act normal in those situations. It's like breathing in high altitude.