Well, in the States it would be called "refrigeration" service
. Your best local source is the local "Yellow Pages", the business telephone directory, unless someone at your marina can give you a reference. The real professionals in this business service the supermarket refrigeration
systems, so you may be able to get a reference at any supermarket (ask the manager) BUT those guys may not be willing to work on anything small at a marina.
You're looking to service what, an engine
system on a sailboat? Or something bigger?