Update

Yes, JtR supports cracking symmetrically encrypted PGP files now :)

PGPCrack-NG

PGPCrack-NG is a program designed to brute-force symmetrically encrypted PGP files.

On Fedora 19, do sudo yum install libassuan-devel -y. On Ubuntu, do sudo apt-get install libpth-dev libbz2-dev libassuan-dev libgcrypt20-dev libgpg-error-dev zlib1g-dev.
Compile using make. You might need to edit -I/usr/include/libassuan2 part in the Makefile.
Run cat password.lst | ./PGPCrack-NG <PGP file>
john -inc -stdout | ./PGPCrack-NG <PGP file>

Speed: > 1330 passwords / second on AMD X3 720 CPU @ 2.8GHz (using single core).

Name		Name	Last commit message	Last commit date
Latest commit History 17 Commits
testdata		testdata
.gitignore		.gitignore
Makefile		Makefile
README.md		README.md
armor.c		armor.c
build-packet.c		build-packet.c
cipher.h		cipher.h
common-defs.h		common-defs.h
compress-bz2.c		compress-bz2.c
compress.c		compress.c
config.h		config.h
convert.c		convert.c
cpr.c		cpr.c
dearmor.c		dearmor.c
dynload.h		dynload.h
encr-data.c		encr-data.c
estream-printf.c		estream-printf.c
estream-printf.h		estream-printf.h
exec.h		exec.h
filter.h		filter.h
free-packet.c		free-packet.c
gettime.c		gettime.c
gpg.h		gpg.h
i18n.c		i18n.c
i18n.h		i18n.h
init.h		init.h
iobuf.c		iobuf.c
iobuf.h		iobuf.h
kbnode.c		kbnode.c
keydb.h		keydb.h
keyid.c		keyid.c
libjnlib-config.h		libjnlib-config.h
logging.c		logging.c
logging.h		logging.h
main.c		main.c
main.h		main.h
mdfilter.c		mdfilter.c
misc.c		misc.c
miscellaneous.c		miscellaneous.c
mischelp.h		mischelp.h
mp.c		mp.c
openfile.c		openfile.c
openpgpdefs.h		openpgpdefs.h
options.h		options.h
packet.h		packet.h
parse-packet.c		parse-packet.c
passphrase.c		passphrase.c
password.lst		password.lst
pkglue.c		pkglue.c
pkglue.h		pkglue.h
plaintext.c		plaintext.c
rmd160.c		rmd160.c
rmd160.h		rmd160.h
session-env.h		session-env.h
status-codes.h		status-codes.h
status.c		status.c
status.h		status.h
stringhelp.c		stringhelp.c
stringhelp.h		stringhelp.h
strlist.c		strlist.c
strlist.h		strlist.h
sysutils.c		sysutils.c
sysutils.h		sysutils.h
tdbio.h		tdbio.h
textfilter.c		textfilter.c
trustdb.h		trustdb.h
ttyio.c		ttyio.c
ttyio.h		ttyio.h
types.h		types.h
utf8conv.c		utf8conv.c
utf8conv.h		utf8conv.h
util.h		util.h