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,…) shop.digitalcourage.de/digitalcourage-und-ccc-auf…