Equivalent to i686 arch of most linux distros, (actually has a slightly more recent instruction set, as i686 is Pentium III), this is likely the older x86 hardware you might want to use.
| HTTP | https://downloads.openwrt.org/releases/packages-18.06/i386_pentium4/ |
| FTP | ftp://ftp.halifax.rwth-aachen.de/lede/releases/packages-18.06/i386_pentium4/ |
See Mirrors for more download sites.