you can get some from FOSS conferences, printing them out yourself is also not bad.

Skate shops. Skateboard companies make a lot of cool stickers.

qwertee.com has great t-sirt designs, but many can also be bought as stickers!

If you want to make them yourself you could get etticett sticker paper, drint or draw on it, laminate it and cut it out.          

Else you could try to find stickers online. Either a service that makes them for you or premade ones, preferrable from artists or "communities".          

As an example a german (has some english, nonlingual stuff) *tech community shop" site where the people running it try to influence politics in a way i like (against mass survailance,...) https://shop.digitalcourage.de/digitalcourage-und-ccc-aufkleber/

Try visiting your local makerspace and see if any of the local people are making cool stickers on the cricut.

Im partial to Etsy. This is a goto for any new laptop I get.

https://www.etsy.com/listing/4350620903/remember-computer-off-y2k-2in-or-3in

Hot Topic

Stickers of what? Because that matters. Etsy and Redbubble have a lot so you’re halfway there. Amazon has them but a lot of that is stolen art. Cheaper but also cheaper sticker material that won’t hold up. They’re trying to maximize profit after all. On the other two you’re typically buying from the artist.

Curious no one mentioned https://www.stickermule.com/unixstickers which is where I got the stickers for my current laptop.

The hottest milfs always have a rad sticker collection

Hey guys anyone know where I can buy some cool stuff? Nah I'm not interested in defining the word cool and what it means to me, you figure it out

I love these ones: https://github.com/mkrl/misbrands

Tattoo artists loooove making stickers

Literally just type "stickers" into your searchbar

Stickers are a form of virtue signaling. Invest in that place/ event/ product and enjoy your free sticker/ self advertising. If you want something personal, invest in an old cricket cutter and create your own design. You can also talk to people who have crickets and ask them/ rent them. "Cool" is defined by you. Put whatever you want on your water bottle.

Edit: Also, I have a cricket. Up to you if you want free stickers. I'm limited. Up to you.