Use this Apple link to get/download older macOS versions. I used it a couple times recently...and it works great:
Thanks Nick.
I downloaded Yosemite and using a Ubuntu computer (I don't have access to another mac) burned the image to a USB key (Nothing I had would unpack it.) after a couple of goes. Etcher failed at first attempt. On the USB key was the .pkg (5.3gb).
When I started the macbook OPTION-R, it read the usb key and suddenly, instead of offering me Lion, it offered Yosemite 10.10.
Excitement! Started the install, but got this message after a couple of minutes
A required download is missing
I found that I could unpack the .pkg, so copied the contents of the
Extract onto the USB key and repeated the exercise above. Again I got
A required download is missing
I'm a bit stumped now.
(MacBook Pro (13-inch, Early 2011))