This recipe is based on traditional conch salad from Nassau, Bahamas. My first substitute when I cannot acquire fresh raw conch is to use frozen or fresh cooked lobster. This is the closest in texture, and is actually a dish made in the Bahamas from Spiny Rock Lobster known locally as crawfish.
If you like you can also use many varieties of fresh fish or scallops, raw. Slice it super thin, toss it in the lime juice for 10 minutes while you prepare the vegees.
Whichever seafood you use the basic recipe is always the same.