The State Deparment recently began publishing online the Treaties and Other International Acts Series (TIAS).  This website is open-access and a work-in-progress. As of today there are only treaties from the years 1996 - 1998.  The treaties are available in pdf.

You can find scanned pdfs of the TIAS print volumes on HeinOnline from 1982 - 1996.

The print volumes of TIAS are available on L1 (KZ235.32 .U55) and, like the online State Department version, have only been released up to 1998.