It’s not as easy as it used to be to find non-Loeb ancient texts, even if you live in a town with a large university. When I tried to replace my OCT Lucretius, I was told that Oxford has stopped publishing that series, so I had to be content with a Loeb.
I believe that the Cambridge Greek and Latin Classics are also no longer being published.
Babae!
I have to replace my books once in a while, because I like to read on the bus, and periodically I lose a book.
you can find plenty of new or used OCTs for sale online but you never know if you’re going to get a nicely printed edition or one of their HORRIBLE reprints that look like xeroxes of xeroxes. 
I troll used book stores so I can see what I’m getting. But then you have to decide if you’re OK with the penultimate edition instead of the very latest. Usually the difference is not earth shattering. I really value quality printing, especially when these old eyes have to distinguish breathing marks. 
The OCT and Cambridge series are still in print and available for purchase:
https://global.oup.com/academic/content/series/o/oxford-classical-texts-oct/?lang=en&cc=us
Actually, the new Loeb Lucretius has a very good text, better than the OCT, but you’ll have to order it from Harvard University Press–it’s not available on Amazon for some reason (or else Amazon is selling the new edition but hasn’t changed its site to reflect the new edition).
Ah, you beat me to it, I was just about to post this same info. Also, while I know that many still prefer the good old hard copy (nothing, in my opinion, feels better in the hand than an OCT), in a pinch there are a huge number of classical texts online reflecting various editions. I have Logos Bible software, which includes the entire Perseus Classical corpus. It’s especially nice when one has a quick need to find a citation. The Teubner editions are also still available, and they have some texts still not available from Oxford.