Broadcast like UDP with the reliability of TCP

Almost all games have a need for the fast-reacting properties (and to a lesser extent, the connectionless properties) of UDP and the reliability of TCP. What they do is they build their own reliable protocol on top of UDP. This gives them the ability to just burst packets to whereever and optionally make them reliable, as well.

The reliable packet system is usually a simple retry-until-acknowledged system simpler than TCP but there are protocols which go way beyond what TCP can offer.

Your situation sounds very simple. You'll probably be able to make the cleanest solution yourself - just make every client send back an "I heard you" response and have the server keep trying until it gets it (or gives up).

If you want something more, most custom protocol libraries are in C++, so I am not sure how much use they'll be to you. However, my knowledge here is a few years old - perhaps some protocols have been ported over by now. Hmm... RakNet and enet are two C/C++ libraries that come to mind.

Take a look at sctp which has a combination of tcp and udp features. There is a windows implementation available.