Of the five players listed in this article, Papelbon and Clippard seem to be the most available. Papelbon will command more in a trade but could prove to be worth it the way he is pitching this season. Clippard and those listed on the Others page will command much less in a trade with a likely AAAA-type player like Michael Choice and a pair of mid-tier prospects.
Any of these additions would greatly benefit a team that is struggling in the later innings due to a weak bullpen. A stronger bullpen will only help the starting rotation that will not be needed to pitch as deep into games to keep leads. If the Rangers are not able to add a starting pitcher to the roster they will need this group to remain as healthy and fresh as possible.