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I received many responses to my request. Most people make their
own. Below are the responses I received:

1. Heinz catsup, Andrews Horseradish (made with water not vinegar) and
   lemon juice. Proportions to your taste.
2. Delmonte Seafood Cocktail Sauce is GF.
3. Fresh horseradish root (peeled, cut into chunks and put in blender),
   mix with Heinz ketchup. May add cider vinegar if you wish.
4. Catsup, horseradish, lemon juice.
5. 1/3 cup ketchup and 1/4 tsp horseradish sauce.
6. Heinz ketchup with prepared horseradish (Boar's Head). Add Lea &
   Perrins Worcestershire sauce and some San-J organic wheat free tamari
   soy sauce. Start with ketchup and just add ingredients.
7. Ketchup with added lemon juice and horseradish to taste. Probably
   halp a cup to one cup ketchup plus juice of one lemon. Then keep adding
   horseradish by teaspoon until spicy enough.
8. Heinz Chili Sauce and add pure horseradish, a dash of
   Worcestershire, onion powder, fresh ground pepper -- we love it. You can
   make it as hot as you like w/horseradish, the plain , ground kind, not
   the creamy type. Let sit to release flavors.
9. Buy kosher horseradish, mix with GF hot sauce, Heinz ketchup and a
   little lemon juice.
10. Mix some ketchup with fresh grated horseradish, squeeze lemon,
   tabasco & worcestershire if you like. I sometimes only use the first
   three and let set for an hour for flavors to blend. The closer to room
   temp., the hotter the horseradish gets.

I have not tried any of these yet because I haven't been able to find
fresh horseradish in my town. Good luck!

Michele