Looking for the porduct name of the yamaha r125 back bearing

Http://www.wemoto.com/bikes/Yamaha/YZF-R_125____YZF_125R/08/
The above site has extensive parts lists. The selection boxes on the right margin will get you to names, pictures, numbers and prices (albeit British)
Start with crankshaft bearing kits or similiar.

The site below has exploded view diagrams and names of the parts in all categories of the bike.
Cheers.
http://www.bikebandit.com/houseofmotorcycles/2008-yamaha-motorcycle-yz125/o/m17114