There are several different ways of getting Freespace.
Of course, there are still a few copies of Freespace 2 floating around, up for sale on eBay, or maybe lying in the bargain bin at your local computer store - although the latter's pretty doubtful. Freespace 2 has not been mass-produced in the states for several years, so checking places that sell used software is your only recourse. Freespace, of course, has been out-of-print (so to speak) for even longer.
Get it from a friend
Oddly enough, Freespace 2 actually has a clause in the license agreement that states that it's legal to give a copy of Freespace 2 to a friend - as long as it's for noncommercial use. So, be nice to anyone who has it, and maybe they'll burn it for you.
Get it from HOTU
HOTU also has Freespace 2 listed in their downloads. Although this download went down for a brief time in the past, it is one of the most reliable ways of getting Freespace 2 over the internet. Unfortunately, the version included with HOTU is stripped-down. Fortunately, it is possible to correct this. By grabbing the missing VP files from a source such as Fractux's FTP, and deleting or renaming the original "data" directory of the HOTU download, you can bring Freespace 2 back to its fully-featured potential.
Get it from another source
There are other sources out there, that may have ISOs of the CDs, the VPs, etc.