Is there anywhere to catch this show from the beginning before the start of season 3? I have heard lots of great things about it but haven't been able to see it at all because I just learned of it.
Each season tells a separate story, with (mostly) separate characters. So watching season 1 or season 2 should not be required to enjoy season 3.
Having said that, there was a connection between season 1 and season 2, including a couple of characters (one of them being the main character in season 2) -- although they were played by different actors because season 2 takes place 27 years before season 1.
But yeah -- I recommend finding a way to watch season 1 and 2, although to finally answer your question, I don't know if FX will be showing them anytime soon. You can see season 1 on Hulu and season 2 on Amazon, but you need to pay for Hulu and Amazon.