I am currently an 8 foot tall juggernaut Warforged fighter in D&D 5e. How can I get to the size catagory large permanently (i.e., 9 feet tall)? There are only two ways I have found so far and that is to be a sorcerer of wild magic, and with wish. But, I am only 9th level, so I cannot use wish. And as stated before, I am a fighter. So I do not know any spells, but I do have my technical “creator” in my party.
Sorry, by RAW, what you've called out in your question is pretty much it.
One of the big shifts that 5E has taken is that making permanent magical changes to something is hard.
In 3.5E, you could use (or have someone else use) the 5th level spell Permanancy to cast a permanent version of Enlarge Person on you. As of 5E, that spell has (at least for now) been left out of the game. On top of that, there are very few canon magical items that imbue you with a permanent spell-like-effect, and none of them impact Size.
At this point, if you really want to make a permanent jump to Large size, you'll need to work with your DM to come up on a solution. Perhaps some Cannith Artificer is willing to upgrade your Chassis to Juggernaut-class...perhaps you can find a magic item that does it. Perhaps you run into an Eldritch Machine (read: MacGuffin) that has that effect.
In short, there is no easy RAW solution that will work for you if you don't get lucky on the Wild Magic table (which could just as easily reduce you back out of Large Size, or even smaller) or Wish (which can by wildly unreliable depending on your DM). If your heart is set on this, talk to your DM and see if you can come to a solution together.
Mixing potions has a 1% chance of making one of the potion effects permanent (DMG, p. 140). If you drink a Potion of Growth (DMG, p. 187) along with another potion, there is a small chance that it could become permanent.
Also, as Bloodcinder pointed out in a comment, this is an optional rule. It is up to the DM whether to implement this rule.