How to do Nikkah when your parents are oppising your marriage?

Assalamu Alaikum , I am a software engineer of age 25. I earn a good amount of money Alhamdullilah. I want to do Nikkah as Islam orders us to do so to protect your iman. I have 2 unmarried elder brothers and my parents says you can't marry before them as its against our cultural norms etc etc. I am trying to find a spouse on my own but no father gives his daughter to a man who is marrying without his parents approval. I am falling into sin and I dont know where to find a good spouse. I tried everything convincing my parents to arrange my nikkah but they are stubborn.