This article is from the Amiga FAQ, by Ignaz Kellerer with numerous contributions by others.
All GCC sources & binaries are available on:
1. Aminet sites (wuarchive.wustl.edu and mirrors such as ftp.luth.se) in /pub/aminet/dev/gcc
2. Ramses The Amiga Flying BBS: +33-1-60037015 HST Dual v32 terbo 4800-21600 +33-1-60037713 SupraFax v32bis 4800-14400 +33-1-60037716 Tornado v22bis 1200-2400 in Topic `Development', Area `Gcc' (are 156).
GNU source code is available on:
1. the same FTP site you've taken the binary distribution from
2. gnu.prep.ai.mit.edu (22.214.171.124) in `/pub/gnu'
3. Ramses The Amiga Flying BBS in Topic `AmigaUnix/Unix/Linux/NetBSD', Area `Gnu Source Code'
These archives should contain everything necessary to get you going, they don't include sources for ixemul.library, which are available on Aminet sites in `/pub/aminet/dev/gcc/ixemsrc3947.tar.gz' (as of this writing, work is in progress for the v40 version of ixemul.library, sources will be available on an Aminet site near you).
As stated by Richard Stallman of the FSF:
"The GPL says that any distribution of binaries must contain either the source code or a written offer to supply source code (see the GPL for details of what is required)."