The way to find a file through dos is to do a dir /a /s and pipe it to find.
This would be the way on a default windows install
dir /a /s c: | find /i "io.sys"
dir /a /s c: | find /i "config.sys"
Just to let you know, IO.SYS and CONFIG.SYS are located in the C:\ directory for a default install. They're hidden system files though, so you'll need to set explorer to see them.