I think they use super filtered water (or they're meant to) so that they don't leave water marks on the windows. Get a ladder and a scrim cloth....

Otherwise there are a number of window cleaning supplies companies online and that includes Amazon/eBay of course.,

I totally get wanting to tackle window cleaning like a pro! A long-reach window cleaner can definitely make the job easier. I recently hired some window cleaning services for my own place, and I was really impressed with the results. They had all the right tools and got the job done super efficiently.
That being said, if you're up for the challenge, buying your own long-reach window cleaner could be a good investment. Just make sure to follow any safety guidelines and maybe start with a smaller area to get the hang of it.