The answer to your question would be that the conjunctive adverb that best connects the independent clauses in this sentence is the following one: Namely. Therefore, the complete version of the sentence would be as follows: Justin was hungry for something sweet; namely, he wanted strawberries.
"Namely" means "that is to say". It is used to introduce detailed information or a specific example. In this case, it specifies the kind of something sweet that Justin wants. He wants strawberries.