iPhone 12 Pro Max

That is correct. Since iPhone 13 Pro and 13 Pro Max will launch this Friday, the 12 Pro/Pro Max phones have been discontinued.

You may be able to find some stock at a carrier store or Best Buy. But Apple doesn't sell them anymore.

I've been around this rodeo many many times. Every year when the new phones are announced, the previous Pro models are discontinued. You may be better off buying the 13 Pro Max, since it's the most current new Pro model you can get. Prices this year, are virtually the same as last year. And its a significant upgrade from the 12 Pro line. SIGNIFICANT.

That I can't advise you about. You'd need to ask your carrier for guidance. I would NOT buy one on eBay, PERIOD. ONLY buy an iPhone for an authorized Reseller. Best Buy doesn't sell unlocked iPhones. So, you may be out of luck on this quest.

Apple releases new iPhones, typically every September. I'm upgrading from iPhone 12 Pro Max to 13 Pro Max. I can't wait to get my new phone. The camera and battery improvements alone are worth the price of admission.