One of these two should work:
https://web.archive.org/web/20150102190950/http://www.r4wood.com/Kernel/a/YSMenu201310.rar
https://web.archive.org/web/20201109205134/http://old.r4wood.com/Kernel/a/YSMenu20171225.rar
If that doesn't work, well, get a new R4 like card or get a 3DS, hack it and use Twilight menu.
I'm guessing installing these is just extracting the folders into the root?