It was only a couple days ago when Nvidia announced its latest graphics cards under its RTX line. While there are still plenty of RTX 2080 and 2070s to be had, the 2080 Ti Founders Edition seems to be in limited supply, as Nvidia has sold out on its own website. Luckily, there are some other retailers carrying it, which means you still have the chance to purchase one.
While it won't be the fastest method, it looks like Best Buy is coming in clutch, offering up different models of the RTX 2080 Ti, including the Nvidia Ti Founders Edition. The unit is priced at $1,199 and has an estimated shipping time of October 8. Sure, that's quite a ways out, but it will probably give you some time to see how the card actually performs, and if you like it, you can keep the order; if not, you can always cancel it. You can also try your luck at Amazon or Newegg, but the former seems to not carry the Ti models and the latter is all out of stock.
Per usual, there are always folks out there trying to make an extra buck, so if you really want one as soon as possible, you can try your luck on eBay, where the mark up is anywhere from a few hundred bucks to over a thousand.