You can access a very similar library (based on a lot of the same sample content, and it's controlled in the same manner) with Garritan Personal Orchestra 5. 

GPO5 is the latest edition, and incorporation of older string libraries is a big part of the package.  This is primarily what makes it different from GPO4.

1.  The GOS Library.

2.  New Pianos.

3.  New Organs.

4.  New Choirs.

5.  A few extra SAM Brass instruments.

6.  Some differences in the way some percussion (Timpani) is controlled.

7.  ARIA Player now has a nice Instrument Tree for easier loading of sounds.

8.  For those who tinker with the sfz opcodes, ARIA now supports using #include lines...so things are organized a bit differently under the hood (and for the better).

9.  Newer versions of ARIA support more opcodes (mainly of importance to advanced users who like to roll their own sounds, or tweak exiting ones at low levels in the sfz files).

10.  Improved support with ARIA for newer Operating Systems and hosts.

GPO5 is played through ARIA.  An advantage to using this instead of trying to get your hands on those old libraries is that you'll be able to use it in Today's range of 64bit hosts.  Using old 32bit plugins can be a tricky process in the latest versions of many hosts out there (requiring special bridges, and still might not work well).

The soundset for it with Finale needs a bit of personal attention to get it sounding as it should (making proper use of the extra keyswitches, and balancing them out in context with your piece), but it does come with a soundset for Finale which gives you a solid 'starting place' to really making it sound good.  The main problem with the Finale soundset for the GOS strings in GPO5 is that it can sometimes conflict with GPO4 human playback entries if you happen to still have GPO4 installed.  It's easy enough to sort out though...

There isn't yet an official soundset for Sibelius, but you're welcome to use my personal soundset as a starting point to shape into your very own if you like.