Look at Zoom but don't attach. The dSLR was never meant to do audio.
If your goal is to shoot video, I would abandon the T3i and move up to a T6s or T7i.
sony 5000 2x double stick bunny with a flap screen fisheye 30 rimster
You would probably Not want to "attach" the two together.
Tascam, Zoom, and Sony make good portable audio recorders.
Prices start at about $100.