I think the OP is in need of the 4.3 version of gnat, found it at a Debian archive site, but lacks some dependencies (gcc and libs). Normally they too should be there around.
The 4.3 versions of gnat/gcc/g++ can be found precompiled in the official Debian 5 (lenny) release for the various platforms. One can get the Debian 5 (lenny) also via the tool "debootstrap" into a chrooted subdirectory, and therein then use "apt-get install gnat" which will install it with all its dependencies (gcc & libs etc.). This works w/o problems at least on a x86_64 platform with i386 target. On his mips32be and hppa2 platform(s) that same procedure should work too. Here are the details: https://wiki.debian.org/Debootstrap
