Right now, that specific data is not available in the API. You can definitely connect to the Streaming API and filter on the hashtag, and you’d be able to start gathering that information for yourself, but this isn’t a feature offered directly in the API. You’d also struggle to find how many times a hashtag was retweeted - you can get that information for native retweets of tweets, but not hashtags.
Have you started to build any code here? my initial response was because I thought you were asking about limited numbers of tweets / results coming back to your application, apologies for any misunderstanding.