Any of the Sri Lankan restaurants like White Oceanic, Majestic, Lakbima and Colombo Restaurant, may have them from time to time. These restos all do finger foods(Or short eats as they are known in Sri Lanka)like cutlets, breaded fried rolls, stuffed bread rolls, stuffed rotis etc that vary in appearance and fillings but can be very similar too.I will ask around and PM ya the exact location of where and when to find fish cutlets specially, but fully recommend you go try these places cos if not the same thing, you may very well find something just as good!