Look down, you have two of them already and they're free!
If that's too much, you can get something like this at most any Japanese / Asian specialty store for several dollars at most (or google "sushi rice mold").
Specialized rice molds are available – this one is for onigiri (flavored rice balls)
Some will make a triangle shape or perfect ball for your onigiri.
If you're making oshizushi you need a press.
There are some electric machines that take rice in at the top and poop out little rice blobs but AFAIK they are all very expensive, aren't as good as doing it by hand, and take a long time to setup and clean.