looking for a type of relay

I am trying to find a certain relay.  I am looking to install a reverse camera and some reverse lights.

I am going to put a switch in to turn on the camera, and also another switch to turn on the reverse lights. 

So on the camera I need a relay that will take two positive inputs but not allow the two to ever connect to each other.  This way the realy can be turned on with the reverse lights positive wire, and also a positive wire from my switch.  But when using the switch, the reverse lights will come one.  I know that I can do this with diodes but I am pretty sure there is a relay that already has the diodes on it.

Same idea for the auxilary reverse lights.  Come on automatically with the stock reverse lights, but can also turn on with my switch.< =text/>