Basically, here in the States, you're going to be looking at TDI or GUE for certifying agencies. I'm not aware of any agency that has a single class covering normoxic, hypoxic and blending into one class, though it isn't hard to find TDI instructors that will run them sequentially for those students who meet the prerequisites. TDI actually has two blender classes, so you'd have to combine four classes to get the full ticket. I don't know if GUE will allow their instructors to combine all the classes.
As has been said a million times before, it's the instructor, not the agency, that makes the difference. I'd start the search by talking to local mix divers and shops about who in your area is offering classes and then begin the winnowing process from that list. I'd also take a look at the TDI and GUE website and familiarize myself with the course curriculum and get a list of qualified instructors from each.
I'm a big believer in training in conditions similar to (or worse) than you will actually be diving in, so think hard before you trot off to someplace warm and wonderful - in the long run it may leave you with gaps in your knowledge that you will struggle to fill in on your own.
I took all four TDI classes sequentially (as you are contemplating) and it was challenging. It took a LOT of my time spread out over a couple of months and required two long weekends of travel plus several evenings of class work. I was very happy with the end result, but I worked like a dog before and during the class. The TDI instructor that I took the classes from can be found
here or
here. He went far beyond the TDI curriculum requirements (important, in my estimation) and was conscientious, demanding, DIR compliant and fun. Even if you don't make it through the entire sequence (do NOT get complacent), you'll come out a better diver.
If you take the blender classes from Greg, you'll learn about assembling a fill station and he'll help you acquire the materials needed. Most of it is in the Global catalog but you need to know what you're doing. Gas comes from a local supply house, I don't have any knowledge of your local distributors.
