Mac Lion “currently unavailable”

hi everyone, this seems to be a common problem but I haven’t managed to find a solution online.

I have a Mac Pro 1.1 which I have agreed to sell. I have followed Apple’s instructions on how to prepare the computer for sale (erase hard drive, deauthorise on iTunes, reinstall OS). But when I come to download the OS, it says “currently unavailable, please try later”.

i have no idea what the original Apple ID would have been (it’s 10-years old) and while my current one is initially accepted, I am told that this may be the issue.

i do have another Mac (a Mac mini).

i don’t believe the Mac Pro 1.1 had internet recovery installed, so I am stuck.

is there any way to fix this?

i suppose I could buy a new copy of Lion on my other Mac and copy to a USB, but I am nervous that this will give the new owner access to my Apple ID/apps/data if I use my account to purchase it.

i am also not too thrilled about paying £20 for obsolete software when the more modern OSX is free. Is there any way to legitamately get a copy of Lion for free given that their systems seem to have failed during the reinstall?

many thanks indeed.