I've just fitted new rear leaves to my 109, and did a fair bit of research due to the high cost here in NZ. I use my truck to run a gardening business, haul trailers, play off road in the weekends and occasionally ferry up to 11 mates around, so needed springs that were going to be heavy duty but still relatively supple for the offroading.
By far the cheapest option was to get parabolics from one of the local parts importers at $550 a pair. But after many phone calls the conclusion was to stay away from them for my purposes. So in the end I got a local spring manufacturer to make a pair of springs according to the Land Rover 3/4 tonne design (with the two overloads), then add an extra two leafs each side. They cost $800 all up but were well worth it. The truck now rides nearly 6" higher than previously at the back (the old ones were pretty shagged), and ~300kg of gear makes no perceptible difference to that. My 33" tyres no longer scrape under any circumstances, the ride at the back is smoother, and the truck is still more stable than a coiler when cornering. All up very pleased, to the point that I will be doing the front ones as well even though the front leaves aren't that bad at the moment.