www.symantec.com/sfbasic

from there, click on "Download Now".
Then click through various License Agreements, etc.
You'll need to create a SymAccount login if you don't already have one.

At one point in reviewing this, I hit an odd screen that said "Accept" or "Submit" -- I hit the "Submit" button, which brought up the list of files. So that part is a bit confusing.

Then choose the following file:
SF5.0 MP3: Solaris x64/Opteron

The other approach is go to www.symantec.com/trialware, but the navigation to winnow the list to just the sfbasic files is more complicated.