Is there any 'switching IC' to replace 'transistor switch' for switching the 12 volts LED array?
What you are asking for makes no sense.  To switch 12 V at 250 mA from a 5 V digital signal, all you need is a FET.  The IRLML2502 would do nicely, for example.  No other parts are needed.  The FET has three terminals.  One goes to the control signal, one is the output, and the third goes to ground.

Any IC is going to require at least a power and ground connection in addition to the input and output signals.  Clearly that's not simpler.  The IRLML2502 is pretty much a ideal switch in this application, so it's hard to imagine what exactly the advantage is of some unspecified integrated circuit.  This FET comes in a SOT-23 package, so you're not going to find a IC that is smaller.  What would this IC do for you that the single FET doesn't?

Again, your request makes no sense.