2i2c has a stickerninja account that can be used to purchase stickers. The username and password for the account are in our team Bitwarden account.
You can find designs meant for printing stickers in the stickers section of our Figma design board.
Look for the stickers section, and at the top are drafts that work well for stickers.
As a general rule, stickers should be about 2 inches in their shortest axis.