You can still find croquettes on diner menus around the country.
Or you can just make them yourself.
Crisco-Fried Tuna Croquettes
recipe from old Crisco advertising
Make 1 cup thick white sauce.* Cool. Add 1 (7 oz.) can flaked canned tuna, 1 tbsp. chopped onion and 2 tbsp. lemon juice. Season to taste. Shape into 6 or 7 croquettes. Dip in egg beaten with 2 tbsp. water, then dip in fine bread crumbs. Fry 3 to 5 minutes in Crisco heated to 365˚ (or when an inch square bread browns in 60 seconds).
* Here's a recipe for thick white sauce from Cooks.com:
3 or 4 tbsp. butter
3 tbsp. flour
1/2 tsp. salt
1 cup milk or one half cup evaporated milk and 1/2 cup water
Melt butter in a sauce pan and whisk in flour and salt until smooth. Gradually stir in cold milk, cooking over direct heat and stirring constantly until sauce boils; reduce heat slightly and continue to stir until sauce becomes smooth and thick. When sauce thickens, simmer for an additional 10 minutes over very low heat, stirring occasionally.
Stir carefully to avoid lumps. If sauce becomes lumpy, use a stick blender or rotary beater to blend out lumps or else press through a sieve. Wondra flour may be used to great advantage since this flour does not have a tendency to lump.