I would like to know that the sentence "if it's sold out" can also be "in the event of book being sold out" or "in case of book being sold out"
and the word "order" can be replaced by " place an order" in this situations( in the book stores)
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Yes, they are fine for the most part. You are missing the definite article "the" and some sticklers might harp on the lack of an 's to show a gerund phrase:
"In the event (or in case) of the book's being sold out, I can place an order in the book store."
Now many writers and speakers will seldom put or say the 's attached to "book" because, first, it sounds stilted and, second, a book is an inanimate object; however, it is correct because "being" is a gerund; therefore, it is acting as a noun therein. Because it is acting as a noun, the genitive case "book's" should be used. Again, I just want to reiterate that this is often not followed in speech and writing, however, and when it is followed, it is usually with people and animals:
"I remember his being a lot older."
"John's being here is much appreciated."
I hope that might have helped you out. Take care and good luck!