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

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.