I'm pretty sure that a replacement brake isn't even available for order from Look/Rossi. So unless you can find someone with an extra one, or some old turntables on Ebay, in a thrift shop, or at a ski swap, you might be out of luck.
Most of what's been stated here is true tough, the FKS 120 has the turntable heel and the P12 toe (multi-directional release, slider AFD, non-metal) while the FKS 155/185 have a toe that will only release laterally, so it isn't as safe in twisting falls (the kind that tear ACLs) but is metal and will last alot longer if you ride hard. Basically it's a trade-off, safety vs. durability...it just depends on what is more important to you and what you need it to do.
"Nothing is impossible. You are only limited by fear and even that you can overcome."
"a simple equation:
force of impact + force of steeze = 0
the two negate each other. for eric, stomping a 60 ft cornice switch is like jumping on a really soft hotel mattress." - ChronicF explaining why Eric Pollard still has knees.