Unfortunately, unless your local bargain bin has a copy of The Lost Treasures of Infocom, then I fear you may be S.O.L on Trinity. But you're sure to find it lurking about on that thar Intarweb somewhere.
If you are interested in further text adventures to try, let me recommend some of the newer ones. The genre's come great strides since the implosion of the interactive fiction (IF) market, and in many cases, the lack of concern for sales had fostered some very experimental and enjoyable titles, ones that would never make it in commercial release. You can rarely go wrong with the winners of the Annual IF Competition (www.ifcomp.org)
My favorite of the 'new wave' of text-based gamery has to be Andrew Plotkin's "Shade" (even though it's at least six years old by now). It's one of the creepiest, most surreal games I've ever played. Also try Emily Short's "Galatea", which is more of a conversation than a game, and Jason Devlin's "Vespers". Enjoy!