Is there a place in Tradedesk where we can see sites that are available for us to serve on?

There's no master list of available sites. Essentially this is based on the campaign targeting, budget, and flight we "bid" on inventory for all the sites. If our bid is accepted based on-site inventory and availability, then we get to serve an impression on that site. But since there's so much that goes into this, we're unable to give them a set list of sites we could potentially serve on. we cannot guarantee specific site delivery - we focus more on where the audience is based on behaviors, demographics, and physical location.