How can I purchase the InDesign software outright without paying for a monthly subscription?

Hi. I have switched from hot metal and foundry type to the IBM Composer to phototypesetting, and again from PageMaker to Quark XPress and then to Adobe InDesign. Each workflow change seemed to be towards a better, more versatile graphics creation environment. For each of these programs, I used to buy every second version released in order to professionally create an occasional pamphlet or book, but I seldom did enough professional graphics work on an ongoing basis to justify paying for an upgrade every 18 months. Now I'd like to upgrade to a newer version of InDesign, and I find that the option to purchase the program outright seems to have disappeared from Adobe’s website, and resellers don’t seem to stock the program either. I went to the Adobe.com/ca site, and I don’t know where the purchase option can be found. I am ready to buy for a reasonable upgrade price — say $150 — but I don’t see any way to do this. Can anyone help?