It's the ML-L3 remote release. Yes, it is very hard to find. I got lucky when I walked into a Wolf Camera just as they got a grand total of 10 in stock (I went a couple weeks later and the guy said they were all sold in one day). But the remote works great, and it will work with you behind the camera, you just have to hold it to the side/barely in front of the camera. I've done it even with the 50 1.8 on the camera, no problems. And if you are inside, say in a studio setting, just point it at the subject as the signal will bounce back off the subject and to the camera, tripping the shutter.
How it works in bulb setting is very cool. You push the button on the remote to trip the shutter, no holding it down. Then you push the button again when you want to release the shutter.
Good luck finding one though. I suggest getting informed by email by B&H when they get it in stock, but be looking for that email, because they go very fast. I mean VERY FAST!! I got burned three times that way. Saw the email but it was too late, once even about 30 minutes after I got the friggin' email!!