Here's a whole lot of rt-11 games, including several versions of Tetris. https://www.sendspace.com/file/4pw39v

Many of these won't run on a PDP-11 -- they were written for clones with framebuffers.

For extra authenticity you'll probably want a terminal which was used with these systems, or its emulation ('15ie' driver in MESS SVN).

There's much more to be said on the subject, ask away :-)