You might try the Loeb Classical Library, described at Wikipedia here and found at this website here. (The rest of this post is about how I searched for this prize.)
So over the last few Christmases (not to mention birthdays), I've accumulated some copies of Greek-language works in the original, for the purpose of practicing the Ancient Greek I have learned. I actually had a hard time finding these Greek-language copies, as you might expect, since the market for these versions isn't a terribly large one in this day and age (although it was once very popular and very prestigious). But I did actually find them, after looking in several of the wrong places first. Since I imagine others might be in the same predicament as I was, I thought I might share my story for readers who are interested. I hope that they might hear of the difficulties of finding copies of these works, and how they were surmounted in a long search for the prize. (This search gave way more surprises than I would have expected.)
Socrates, one of the people I wanted to read about in Greek
I had never taken a Greek class before I started my search, and still have not taken one since that time, either. Thus, I had no professors to tell me where to look, and decided to go online to use a search engine. I went through one webpage after another trying to find them, and compared many versions on Amazon to see if they had the original Greek or not. When they listed a translator, though, I stopped investigating that version right then and there; thinking that if it had a translation, it must not have the original Greek. So when I first came across the Loeb Classical Library, therefore, I initially ignored it, because their versions all listed translators for their works. It turned out that this was a mistake, you see, because these versions actually had the original Greek in them side-by-side with the translations they mentioned. Thus, the prize had been under my nose the whole time, and I didn't see it.
Ironically, I continued searching elsewhere in less fruitful places, and became increasingly disheartened at my seeming lack of progress. After a while, I started to think that I would never find the original Greek for the authors I sought, and would give up temporarily in my search only to resume it later with the same result. I ran across a website called LoebClassics.com which had the text of them online, but which allowed only so many free viewings per month, and charged its viewers for any additional viewings. Not sure that I wanted to pay this monthly fee, I kept on looking, with newly-acquired hope about it being "out there somewhere."
Plato, author of many of the Greek works I was then seeking
One day, I was just comparing versions without regard to whether they listed translators for their versions (just for my own amusement), and I came across the print version of the "Loeb Classical Library" on Amazon again. Or more accurately, a collection of different print versions of various works from Ancient Greece; with one Amazon page for each volume. When I read the reviews, I discovered with some pleasure that these versions had the original Greek in them side-by-side with the translation! This explained the mystery of how they could accurately list a translator at the top of the webpage, and yet still have the original Greek in them nonetheless. After this "eureka" moment, I had finally come to the end of my search, and it had been several months (possibly even years) with little or no progress in my search.
Specifically, the versions I found had the Greek on the left page and the English on the right page. This made it easy to read the two languages side-by-side, so that I could compare a translation to the original as needed. I found the long-awaited copies of the specific works I had wanted, and read the Wikipedia page about the Loeb Classical Library to get some more information. There was all kinds of information available, including a list of Greek and Latin authors that were included in the collection. Works in Greek had a green cover, it said, while works in Latin had a red cover. And the variety of each kind of work was astonishing, with works in all kinds of genres that showed the breadth of classical learning. (Literature, philosophy, history - all there waiting for someone to read them.)
Xenophon, another author whose Greek text I would later seek
I am not trying to convince anyone to buy these things, I should make clear, since I know the market I represent is in a small minority. But I mention this as a personal experience with the subject of ancient history; and hope that it might prove (at least somewhat) interesting for others; even if they are not in the market themselves.
If you liked this post, you might also like:
My search for the Greek New Testament
Why I am learning Ancient Greek
Falling in love with Classics
Learning the basics of Ancient Greek