It's not going to be a separately available part.  If it's part of the touchpad itself, you'll need another unit that comes with the latch.   If it is part of the system board, that's more difficult -- your best option there is to look for someone selling an otherwise dead mainboard on EBay for a low price, and salvage the connector from the donor board.  
Hello i have an Alienware m15 R2, and yesterday i had to replace a Fan that failed, but whe i was puting everything back together i broke the "little black plastic clip" that keeps presure to the cable and the mother board.  And now my trackpad does not work i have a HID 10 error, the cable is in place i used tape to keep it in place, but i guess that it needs the presure that the clip gives to the cable to work properly. Can some one help me telling me where i can purchase this clip.   Regards,
m15 R2, where to find "little black plastic clip" for Touchpad cable to the 
motherboard