Knock Knock, another knock question... Options

[946thGenGT]

Recently I've been experiencing a rather annoying knock that seems to be coming from the rear left wheel or at least that area. The knock, when it occurs, increases as speed does and is not affected by engine RPM. It seems to start after I've hit a bump or taken a corner, and is solvable every single time by bringing the car to a stop and then starting again. I've taken off the wheel to see if I can notice anything wrong but it all seems to be in good order to me. Anyone have ideas? Do I just need an alignment maybe?

[946thGenGT]

It doesn't knock in turns, it knocks after turns, repeatedly. And looks like I've found the problem... I thought it was the rear left wheel, but after today I'm pretty sure it was the rear right wheel. Was walking up to the car and noticed that my rear right wheel had only 3 lugnuts on it... and the 3 that were on it were kinda loose. I tightened it up and then moved a lugnut from my rear left wheel onto that one so I had two wheels with 4 instead of one with 3. The rim is still in good shape thankfully. The two lugnuts that had come off weren't side by side so there wasn't really any excess pressure on one part of the wheel.

So I went to a couple places to try and get lugnuts... Nope. I showed them what I needed and they all told me that I would have to go straight to Toyota for them but knowing Toyota they'll be $20 each or something. Anywhere online I can get them cheap?