STLport project don't provide binary (or other) packages for specific distribution. But you can find it in distributions or from other places. Note, that STLport's developers don't responsible for maintanance of this packages.

Debian

Debian packages. Present in stable line too, but old and with wrong reference information.

Gentoo

Gentoo ebuilds.

Symbian

Marco's distribution for Symbian.

FreeBSD

FreeBSD portages contain unsupported obsolete vertion of STLport. So no reference to it.