In reply to Tom Ripley Mountain Guide:
Yes. Lima, at the outdoor shop in Larcomar, Miraflores shouldn't be a problem, though there may be some lying around in some hostels as people have left them there. It'd be much easier to get them from Huaraz, Jo's Place does very good rates on ones that have been left by people leaving.
I used my gas stove for everything in Peru, the only thing I'd consider going through the hassle of taking a petrol stove for is melting snow. Canister management was important too, it's easy to use loads of gas by using a cold canister, so on summit day it'd be in the bag with me and my boots to stop it from freezing. Warm hands around the canister help when cooking too, though Andy K suggests a copper wire in the flame then wrapped around the canister which is similar to bomob making, so needs watched.
Why are you going to Juliaca? There's not much there, unless you have designs a bit south...