I'm not a fussy eater, but I am selective. if I'm a regular at a restaurant, I typically have some item I order every time. This works well for me until my favored item is dropped from the menu. Now what?
One option is to turn this into a small adventure. I could look for something new. After all, new menus are created for a reason. In some cases, this may be the only choice. If a burger chain drops a sandwich from the menu, it is probably gone. If the item requires a seasonal ingredient, there may not be an acceptable substitute. There are valid reasons for dropping an item from a menu, on which case it's best to smile and look for something else.
Other times, a restaurant is willing to serve items it has taken off the menu if you ask politely. In this case, the only real constraint is your being willing to ask. In a sense, this is no different than asking for special preparation. In the worst case, they will say no or quote a different price.
It doesn't take much imagination to understand that your life will be better if you stop assuming against yourself and ask for what you want, but there is another side to it that is a true key to success. To understand it, you need to look from the provider's point of view.
A couple months ago, I stepped into a small Greek restaurant in my neighborhood, something I've done a couple times a month for the past few years. I'm nowhere near being their best customer, but I am a regular and the manager knows me by name. When he saw me, he came to my table and told me that my usual sandwich was no longer on the menu. "But don't worry," he said. "Ask anybody and they'll get it for you." He had proactively solved my problem and protected a customer relationship at no cost whatever. If you want to succeed, don't just give the customer what he wants, encourage him to ask.
Zig Ziglar had it right when he said
"You can get everything in life you want if you will just help enough other people get what they want." This gets easier for everyone when you ask.