8.1 is in self service support and its downloads are no longer available from NetApp support site.
For 8.2 you can download the 8.2.5P3 release which is the latest one and bring both controllers to that version; please beware that in this stage you will not be able to perform a non-disruptive upgrade due to the inability of performing takeover at the moment.
unfortunately we do not offer old software (not just ONTAP) when it's past the end of support date.
Please be also aware that 8.1.4 has also not been updated in a while with regards to security fixes: if you have a custom application developed for it, then indeed you will have to confirm it's still compatible with 8.2.5P3 or upgrade it as needed.
Hi, you can take the files from /etc/boot/x86_elf on the working controller then netboot and install the new one with these files. (you can also copy them to the other flash card if you have a reader).
Here's how to set the partner to be a netboot server.