Although it's not listed specifically for the G751JM, you have a couple options if you want to get the 180W AC adapter from ASUS in the United States.
If you can reach them, you may want to confirm the 180w adapter will work for the G751JM just in case you run into any problems, but they do list other 'G' series notebook models that use the same adapter so should be fine.
1. (U.S.) 'ASUS Store' (cheaper?) -
http://store.asus.com/us/item/201412AM300000085/A19419
2. U.S. and Canadian ASUS 'eStore' -
http://us.estore.asus.com/collections/ac-adapter/products/0a001-00260100
