"Windows 7 isn't easy to purchase anymore, if at all."
Yes, but there are ways to find a copy if you're willing to put in the effort. Try this plan:
1) Go to obscure online retailer www.amazon.com.
2) Search for "Windows 7" in Software - the site search engine should automatically recommend this department.
3) Buy the item at the very top of the page.
It gets slightly more complex if you want Pro or Ultimate. Then you have to perform an intermediary step where you scroll down to find the specific item you want, as it is further down the first page.