You’re looking for the old VSTi plugin version which is here: HALion Symphonic Orchestra 1.5, however that’s only the VSTi and not the content. If you still have the Cubase 5 installation DVDs, the demo is on that and as long as you have the license still on your USB-eLicenser, it will work.
If you download and install the HALion Symphonic Orchestra VST Sound Instrument Set it shows up as a library in HALion Sonic SE and your license will also allow that to work. That download has the sample content, which is basically the repackaged 16-bit sample set of the original (the 24-bit sample set was never repackaged).
I would advise to move away from using the old VSTi even though it will work in the 64-bit version. The problem of course is that old projects that use it will not work without it … you’d have to adjust all your tracks to point to HALion Sonic SE and try to match the patches.