Are you in control of the whole building? It'll be tough if you aren't.
If its a commercial kitchen the health dept may dictate what to use. Don't screw around with "natural" stuff and risk getting shut down
Start by plugging every hole..every space around a pipe where t hey can enter. Might involve pulling out dishwashers etc.
Traps aren't really practical because you have to keep emptying them. Poisoned bait is very effective.