For the dip: Combine the mayonnaise, sour cream, buttermilk, vinegar, dill, parsley, garlic powder, onion powder and a pinch salt in a medium bowl. Taste to adjust seasoning as needed. Hold until ready to serve with the fritters.
For the fritters: Grate the zucchini into a large bowl lined with a dish towel, then wring out to remove as much excess water as possible. Discard the liquid and add the zucchini to the bowl. Toss together with the artichokes, fontina, Parmesan, parsley, cayenne, 1 teaspoon salt and 1 teaspoon black pepper.
Add 1 inch of oil to a large cast-iron skillet, filling only halfway. Preheat the oil to 360 degrees F. Fit a baking sheet with a wire rack.
Sift the flour and cornmeal together and then toss with the zucchini mixture to evenly distribute. While stirring with your hand, slowly add the seltzer a little at a time until a sticky batter forms. You want the ingredients to hold together so the fritter will float in the fry oil.
Test the oil for readiness with a pinch of the mixture; if the oil bubbles up it's ready. Using a heaping teaspoon or a teaspoon-size ice cream scoop, add no more than 10 fritters at a time to the oil so it does not overflow. Fry until golden brown, flipping halfway through, 2 to 4 minutes total. Use a fish spatula or slotted spoon to transfer the fritters to the prepared baking sheet and sprinkle with salt. Repeat with the remaining zucchini mixture. Serve warm with the farmhouse dip.