MacPorts might have them, although I didn't know that Darwin used the BSD linker. Neither FreeBSD, NetBSD, or OpenBSD use the BSD linker. They use the standard GNU binutils along with GCC. I don't think it'd be as simple as downloading binutils and installing though because the Darwin build system is heavily tweaked, so I'd say binutils would actually require certain modifications to work on Darwin. The question remains whether somebody has actually made those modifications. The places to look are pkgsrc, MacPorts, Fink, and possibly Gentoo-Portage. If pkgsrc doesn't have binutils for Darwin, then I doubt the other three do.