Where can I buy a replacement screen for my iPhone X? I see different screen types, LCD, OEM, OLED - which one is the proper one to get and who can I buy it from?

Unless you are an Apple Authorized Service Provider, Apple will not "sell" you an authentic iPhone display screen. Any other replacement screen would be a non-Apple product. Using such a screen would void any warranty and could cause more issues than resolve them. I would suggest that you contact Apple Support directly and arrange to get your iPhone repaired properly. To do so, just use the "Get Support" link in the upper right-hand side of this forum's web page.