i want a 45 Mhz 3ch Rx note:
this must be the rx of a 45 Mhz   3ch coaxial heli. ....
Since my nephew crashed his heli and had been crying the whole day and half an hour ago he came to me for help
please friends help us ......ur little help can help my nephew

Practical solution, buy a new 3ch heli.  45Mhz is very very very uncommon, plus on 3ch helis, it is never an RX alone, it is usually an "all-in-one" unit. 

You can try posting the model details (exact make and model number) of the heli, so that others can try to see if there is anything on eBay etc (or if it is the Model Art one).

i was gifted by me  only...and i am not in a position to buy another one for them

The issue is that except for a few models like the Model Art one (even that one may be a hit and miss!), these helis are treated as "disposable" toys, so finding parts becomes a real challenge.

Like I mentioned earlier, you will have to be very specific about the model number and other details for others to try and see if anything is available.