First, you may already have it if you have gcc for your platform; g++ and gcc are combined now (as of gcc version 2.0).
You can get g++ from a friend who has a copy, by anonymous FTP or UUCP, or by ordering a tape or CD-ROM from the Free Software Foundation.
The Free Software Foundation is a nonprofit organization that distributes software and manuals to raise funds for more GNU development. Getting your copy from the FSF contributes directly to paying staff to develop GNU software. CD-ROMs cost $400 if an organization is buying, or $100 if an individual is buying. Tapes cost around $200 depending on media type. I recommend asking for version 2, not version 1, of g++.
For more information about ordering from the FSF, contact gnu@prep.ai.mit.edu, phone (617) 542-5942 or anonymous ftp file `ftp://prep.ai.mit.edu/pub/gnu/GNUinfo/ORDERS' (you can also use one of the sites listed below if you can't get into "prep").
Here is a list of anonymous FTP archive sites for GNU software. If no directory is given, look in `/pub/gnu'.
ASIA: ftp.cs.titech.ac.jp, utsun.s.u-tokyo.ac.jp:/ftpsync/prep, cair.kaist.ac.kr, ftp.nectec.or.th:/pub/mirrors/gnu AUSTRALIA: archie.oz.au:/gnu (archie.oz or archie.oz.au for ACSnet) AFRICA: ftp.sun.ac.za MIDDLE-EAST: ftp.technion.ac.il:/pub/unsupported/gnu EUROPE: irisa.irisa.fr, ftp.univ-lyon1.fr, ftp.mcc.ac.uk, unix.hensa.ac.uk:/pub/uunet/systems/gnu, ftp.denet.dk, src.doc.ic.ac.uk:/gnu, ftp.eunet.ch, nic.switch.ch:/mirror/gnu, ftp.informatik.rwth-aachen.de, ftp.informatik.tu-muenchen.de, ftp.win.tue.nl, ftp.funet.fi, ftp.denet.dk, ftp.stacken.kth.se, isy.liu.se, ftp.luth.se:/pub/unix/gnu, ftp.sunet.se, archive.eu.net SOUTH AMERICA: ftp.unicamp.br, ftp.inf.utfsm.cl WESTERN CANADA: ftp.cs.ubc.ca:/mirror2/gnu USA: wuarchive.wustl.edu:/systems/gnu, labrea.stanford.edu, ftp.digex.net:/pub/gnu, ftp.kpc.com:/pub/mirror/gnu, f.ms.uky.edu:/pub3/gnu, jaguar.utah.edu:/gnustuff, ftp.hawaii.edu:/mirrors/gnu, uiarchive.cso.uiuc.edu:/pub/gnu, ftp.cs.columbia.edu:/archives/gnu/prep, col.hp.com:/mirrors/gnu, gatekeeper.dec.com:/pub/GNU, ftp.uu.net:/systems/gnu
The "official site" is prep.ai.mit.edu, but your transfer will probably go faster if you use one of the above machines.
Most GNU utilities are compressed with "gzip", the GNU compression utility. All GNU archive sites should have a copy of this program, which you will need to uncompress the distributions.
UUNET customers can get GNU sources from UUNET via UUCP. UUCP-only sites can get GNU sources by "anonymous UUCP" from site "osu-cis" at Ohio State University. You pay for the long-distance call to OSU; the price isn't too bad on weekends at 9600 bps. Send mail to uucp@cis.ohio-state.edu or osu-cis!uucp for more information.
OSU lines are often busy. If you're in the USA, and are willing to spend more money, you can get sources via UUCP from UUNET using their 900 number: 1-900-GOT-SRCS (900 numbers don't work internationally). You will be billed $0.50/minute by your phone company.
Don't forget to retrieve libg++ as well!