Answer: Wow! You are an inspiration to me! I've been thinking about taking some classes, and I think I'll call today!
Because textbooks change from year to year, I doubt that the ones I used will still be available, or in general use at colleges. For example, Brady's "The Nature and Property of Soils", Tisdale's "Soil Fertility and Fertilizers". I think your best bet would be to contact the nearest University that offers the courses you want, and ask what texts they use. You might try to go in person; if you explain your situation, it's possible they could help you figure out a way to pursue your dream! Maybe you could audit courses for a small fee, for example. Or work out a work-study situation. (I actually took a relatively low-paying job at a University so I could take classes for free!)
Have you considered some of the "distance learning" opportunities now available? I found a few web sites that might interest you. Try searching the web using the words like "distance", "learning", and "horticulture".
By the way, NGA offers a two-part online course called "Exploring the Garden". This covers all the basic botany principles, and uses examples from the garden to illustrate key concepts. It's probably a little more in depth than your master gardener training, but isn't a rigorous, University-level botany course.
The best of luck to you!
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