Excuse me, when is the honorific imperative sentence used in Japanese? For example, is it more polite to say "くださぃ"?

Well, you have a question. Honorific words are a form. How can there be an order? Imperative is imperative, honorific is honorific, not the same thing.

The prototype of くださる you mentioned later is くださぃ. There is no more polite question. くださぃ itself is very polite. A more polite way of honoring is: くださぃませ. It is usually placed at the end of a sentence.