souurce for old version of libffi

[tim.beech]

I'm packaging GHC (Glasgow Haskell Compiler) for Salix, a Slackware
derivative, and it depends on old versions of libgmp and libffi.

Specificaly, it is looking for /usr/lib/libffi.so.3
and finding libffi.so.6

These numbers don't seem to correspond to the version numbers for
libffi; as far as I know, the latest libffi for Slackware is
libffi-3.something.

I've searched without success. I'd be extremely grateful if anyone could
point me in the direction of a tarball.