If you are stuck on Creality, you could get it from their official store at https://www.creality3dofficial.com/p...-s5-3d-printer

But have you looked at other brands and models? The Artillery Sidewinder X1 is 300 x 300, so slightly smaller, but a great option as well...and I'm sure you'll get other recommends around here.
I have a Sidewinder and a Creality Ender 3 Pro and enjoy both very much, but you'll shortly see Aardvark direct you away from Creality (they're his cryptonite), but he may have some better suggestions as well.