Sadly nowhere. I've gone back to having multiple devices, a Nexus 4 for apps/browsing, an iPod nano 2nd gen for music, and at times an iPhone 4 for phone calls, sms and email. I can't use a device with extra tall aspect ratio like 18:9 or a notch or rounded corners on the actual display.
I had thoughts of making an old iOS style UI for Android, but came to the conclusion that Android is too f*ucked and poorly designed, it just will never work right.
I also share your enthusiasm for the old GUI's, I used to love everything Apple did, but at this point I don't see myself ever buying anything from Apple ever again.
For me it wasn't just the old iOS, it was also Objective-C that I loved, it's still my favorite programming language to use. When they went to Swift, that was the nail in the coffin.
But I actually prefer iOS 5 over iOS 6. I bought a couple of old iPhone 4's (not the 4S, the 4) because it's possible to downgrade them to iOS 5 (or iOS 6 actually). I think the 4S is no longer able to downgrade.
I am writing an X window manager that imitates the old Mac Classic GUI to some degree and parts of the old iOS interface (as well as other classic GUI's), if you're interested you can take a look at hotdoglinux.com. I've been thinking of putting together some kind of Raspberry Pi distribution with a touchscreen interface, but we'll see.
You wouldn't need to become a billionaire to do that though, it's not that hard