Ballistic Addon Studio is no more, as of July 2004, but their addons live on, here at The FAQ and at many other popular OFP sites. To make life easier for the OFP community, I've listed below every official BAS produced file I know of, the latest releases and for OFP Resistance and OFP GOTY versions only. If you see something missing, call on me!
In October 2004, OFP reg Pappy Boyington published the BAS Website Reborn. The site uses much of the graphics artwork that was incorporated in BAS' original website. You'll also find general information and README documentation there about each BAS addon. Eventually, Pappy will also mirror file downloads for all of BAS' addons and missions, as I've done below.
Addons:
BAS Blackhawks and SOAR Pilots
BAS Repair PBO - fixed (unofficial)
BAS Tonal Island and OPFOR Units (includes JAM2) (link temporarily out of order - look here for other mirrors of this file)
Missions and mission packs:
Littlebird Demo Mission (unofficial - modified to use BAS Delta and Ranger units)
Spec Op Mission Pack (unofficial, by BAS mission maker Nagual)