ftp://ftp.cse.buffalo.edu/pub/FreeBSD-Archive/old-releases/i386/3.5.1-RELEASE/compat21/  direct

158 B  1998-09-21install.sh  1000+ mirrors
268 B  2000-07-19CHECKSUM.MD5  950+ mirrors
235.00 KB  2000-07-19compat21.aa  300+ mirrors
70 B  2000-07-19compat21.inf  154 mirrors
203.46 KB  2000-07-19compat21.ab  61 mirrors
1.36 KB  2000-07-19compat21.mtree  11 mirrors