Can you do 72"?

https://www.potterybarn.com/products/classic-double-wide-mirror/?pkey=cmirror-medicine-cabinet-storage&cm_src=Quickbuy

It needs to be at least 75 so we can see ourselves when in front of the sinks, but thank you for the link!

You can go to your local glass and mirror guy they can custom cut one for you and you can go to the local box store and get some wood to create a frame for the piece.

I suspect you'll have to go custom because the odds of finding a mirror that size with the right proportions just sitting around waiting to be bought are slim. Also, it's going to be hard to find sources online that have that huge a mirror as a standard item and are willing to ship it...unless they charge a huge amount for crating it.

Get mirror cut at lowes or home depot, buy wood molding cut it to make picture frame around.

There's an online company called MirrorMate where you can custom-order a frame to fit an installed mirror. You would get the mirror from a glass company, who will mount it for you, which I wouldn't attempt myself with a mirror that large.

https://www.mirrormate.com/