What you are looking for is called Discovery. Once the lawsuit is filed, you will enter a phase of the lawsuit where each party asks each other for evidence related to the claim or reasonably believed to lead to evidence.
So yes, you are asking the defendant company to provide evidence of their own violation. And if they do not cooperate, you ask the court to compel them to.
And no, you cannot quote anonymous post from another website as evidence, that is called hearsay.
You should spend more time studying how to file and win a lawsuit, or hire an attorney before you proceed.