I did a bit of poking around last night, and so for anyone who's still seeing the "you already have all the games in this order" error, there may be a temporary solution, although I'm not sure it will still work when the sale is over.
Instead of trying to buy the packs you want though your game library, or searching for them directly, open the Origin app and then click on the "Celebrate Black Friday" banner across the top of the Origin window. (It doesn't always show, but clicking on Browse on the left of the screen usually made it appear for me.) This will bring up a list of all discounted games, which is a lot; you can use the "sort & filter" function in the upper right corner to narrow the list. I used "simulation." Then you'll be able to click on any TS3 EP and select "Add to Order" instead of "Buy Now," and you'll see a Buy button towards the top of the screen. You should be able to buy all the EPs you want, although SPs won't be available through this method, since they're not on sale.
It's hard for me to test this approach, since I already own all expansions, but it did work for someone else's account. If any of you are still having trouble, hopefully you can use this workaround to buy the content you want before the sale ends.
