Spyderco is Left-hand-friendly Central. Their lockbacks, ball-bearing locks, and integral compression locks are all ambidextrous. Their phantom lock can be ambidextrous with a bit of adaptation. Get your brother a Delica, Native, Endura, Spyderhawk, and, when they come out, an A.T.R. and Dodo. There are several others, but you'll need more money after making that purchase. There are also ambidextrous knives from other companies as well, but the comparable models cost more. For pure function, get your brother a Delica. For looks and function, call your brother an ingrate and then get him a Delica or don't call him names, but get him a Native. You can't go wrong with either.
For being such a good brother, get yourself an ATR when they come out or buy a Benchmade 921 Switchback or their 806D2 knife.
Edited to add:
When the plain-edged Calypso Junior is re-released under a new name, buy two so that you and your brother can have matching, ambidextrous Spydercos.