One of my favorite places to buy Raspberry Pi supplies used to be Element 14... which was bought out by Newark which is part of a bigger conglomerate called Avnet. In the end nothing has really changed and Newark is a great place to purchase Raspberry Pis, Compute Modules, and assorted Raspberry Pi gear. They usually have good stock and typically show you when stock is expected. (Currently they are low on the Raspberry Pi 4 2GB model but have 2000 on order for 9/27.) Here is the link to the item: Newark - Raspberry Pi 4 2GB
This link is direct to there Raspberry Pi product page which has all the different Raspberry Pi models listed and some Raspberry Pi essentials like cases and power supplies, HATs and Add-ons as well as a project page.
Newark.com - Raspberry Pi Product Page
Check it out and let me know what you think.