You can download the game here: http://eisonline.classictw.com.
It looks like you can get a single-player vs AI version or purchase additional licenses to allow remote access:
To celebrate 25 years of TradeWars, EIS is releasing a special 25th anniversary edition of TWGS. This new release features a free starter package that includes support for one active TradeWars game and a single remote connection. Practice your trading skills and compete against AI-controlled alien races, explore the editors and create your own custom aliens, planets and ships. The free starter package is fully functional, including all TWGS functionality as well as every TradeWars feature, even the Gold extensions!
If you decide you’d like the flexibility of running more than one game at a time, or you’d like to support more than one remote connection, simply order as many additional game slots ($2 each) and player connections ($3 each) as you need (limit $10 per order). This new pricing model is designed to allow anyone to explore this classic game for free, while continuing to place a premium on large publicly hosted sites.