Where to download W7 SP1 install file

Sorry if this has been asked a zillion times, but I did a quick search and didn't see it.

My friend has W7 but never installed SP1. He said that Update warned him that SP1 was no longer available, but he could not do the W10 update without it. I figured, no problem, I'll just go to the download page and download the SP1 install files (32 and 64 bit, for whichever he needs).

Alas, the download page MS, itself, directed me to was no longer.

I'm not sure if MS has oddly enough pulled the updates for W7, even the requisite SP1, but I'm sure these files exist, elsewhere, nonetheless. So... where best to download?