After staring down find(1) on an AIX system I regret not going down the du | grep path. At least that way I wouldn't be stuck trying to mash GNU's parameters into completely incompatible version of find.
If your system supports `man 1p` (loading the posix manual for each supported utility), it is a good idea to reference that instead of the default manpage; it is more likely for your utility to support posix options than GNU extensions in legacy and non-linux systems.