If the posts will be posted anytime in the future, you can set up a Tracker. When started, a new Tracker will gather up to 5,000 tweets/posts from the past 30 days, and continue to gather posts in real time moving forward. Trackers are available through a Union Metrics subscription.
If the posts were shared less than one month ago, then you can access them through a Union Metrics subscription. A new Tracker will include up to 5,000 post from the past month when you start it up.
If tweets were posted more than 30 days ago, that historical data is no longer available through any Union Metrics self-service subscriptions.