whats the best way to reach owners or decision makers of restaurants and caffes?

any good tips how to reach this particular group of people?

Best way depends on the town/city/environment/country - and the size of restaurants/franchise/etc.

Here are a few ways.

1. Association & townhall meetings - [You get a few at the same time]
2. Having a meal there on a weekday
3. Getting to know their main suppliers (Fresh food, wine resellers, et al)
4. Through a good real estate agents who cover the areas for high traffic business locations
5. In some places, there are placement agencies for waiters/waitresses/kitchen helpers - these placement agencies will usually deal directly with the owners/decision makers on staffing.
6. IT companies that sell point-of-sales systems to restaurants

Go eat there. Ask the staff to speak to an owner.