The third one is really not an option, though, when ordering ice cream at a restaurant. It is, however, what you might say at home if you were being served ice cream, maybe in answer to, "How much ice cream would you like?" "I would like two helpings, please".
Although it is not the best English, in NYC it is very common to say "Give me (gimme) two ice creams, please."
For the avoidance of doubt, "I would like two ice creams" is pefectly natural, at least in British English, and is what you would say in an ice cream parlour if you were buying for two people - or if you were buying two for yourself! We would never say I'd like two orders of ice cream.
Usage varies but it appears the two most common spellings are "ice cream", as two words, or "ice-cream", hyphenated, rather than a single word.