There is one great site where you can download games for your TI-83:
TI-83/84 Plus BASIC Games - ticalc.org
Just download the software (if you need it) and transfer the files over to your TI-83. After that, press PROGRAM on the calculator (could be abbreviated) and have fun.
*Note: I did that for TI-83 that isn't the plus edition but I'd imagine it'd be at least similar. I'm sure there are more details instructions on the official Texas Instruments website.