Capt C,
Something I've been looking at doing for a couple of years myself, in the opposite sense (NZer in the UK flying for a charter/lowcost airline)
all I can suggest is contact the likes of the people you mentioned...it may also be worth having a look at aviationjobsearch (its a website) as there seems to be plenty of summer contracts offered.
The downside for you is that they are mostly on jets...the plus side is....6 months on a UK salary (contract) would mean 6 months off in the NZ summer
with cash too spare.