What postal services that offer printed stamp labels? To give you an idea, here are some examples
Germany: https://www.deutschepost.de/de/i/internetmarke-porto-drucken.html
France: Imprimer un timbre : Mon timbre en ligne personnalisé - La Poste
The United Kingdom offers online postage, that you can print yourself. If that is what you mean 
Canada offers a printed stamp label; but it doesn’t look like a stamp. It looks like a label. I use it when an envelope is large/heavy or on parcels.
It is available in the Netherlands too.