Nowhere. That is, the title of the comic does not refer to any REAL Rapid City. It's all made up. You can tell by all the superheroes there. But, if you want to find Rapid City on the web, there are several ways to do it.
Follow on Facebook.
Follow on Twitter.
Read fully illustrated Rapid City at Champion City Comics.
If you have something to say about those illustrated issues, use any of teh above, or the Rapid City discussion thread at Panels on Pages.
Link to me, follow me, like me, read me, and if you have anything to say about Rapid City (good or bad) please use your favorite social media outlets to do so.