Well I finally found my SE 64gb, white SIMFREE. I had to check a few times daily but it popped up on one of the 5 Apple stores near me and I grabbed it. Crazy how constrained these are
Glad you found one in the end. I just wanted to say for anyone else who has searched this thread and couldn't find one, that they are still available all over the world, but we often find that it's harder generally to get the 64GB size in stock, but let you special order still. For some stores it's because the 64GB model always sells out faster, but for many I have noticed that they never stock them to begin with. (I found this to happen with previous models of iPhone aswell) Some stores would always have them in stock, and others just limited the 64GB models top special order as a company policy. So sometimes you just need to know where to look.
Now I appreciate that you'd probably not want to travel all the way over here to Greece just to find an iPhone, but my point is merely that if you don't get success at the first few places you try, not to give up because broadening your search both locally and internationally, you will come across one eventually. In order to help make this much easier though, I'll offer a practical suggestion that I have used myself which would be available easily to literally everyone....
For example, there are literally TONNES of sellers on Amazon who nearly always have stock of these. (if you can't find them on the global Amazon site (amazon.com) there are plenty of other countries of amazon, and each have their own set of suppliers, fulfilment centers, and different third party vendors. If you need the site to be in English, amazon.ca (canada), amazon.co.uk (england), amazon.in (india) all have sites in English. If you don't find any on these, you could even try the non English versions and just paste the web address into google translate, and it will automatically translate the whole web page into English. (I have ordered from Germany and Italy many times using that method, and it worked just fine!) So these are a few other nice ways to find suppliers very easily, for just about anything. iPhones are always sold on there. (and you usually find many sellers on there for nearly every size and color of iPhone). You'll often even find older models (aswell as the most recent). If you find however that they don't deliver to your area, the quickest way to see which vendors ship worldwide is to look at the various sellers for if it says "Domestic" (which only ship locally) or if it says "International and Domestic" (which usually ship worldwide). Also, as there are a mixture of people who sell used models versus brand new models, to filter to just the ones that say "New", and to also read the "condition note" section, as they will often tell you which ones are brand new and boxed, versus ones that are just selling "as new", "used", or "Refurbished", etc. I would also advise to check the sellers which ones are established businesses rather which ones are just one-man-bands selling their own personal model. Phone companies are generally a safer bet.
Another caveat to the amazon approach though that I would recommend to be vigilant on, is to check the ratings of the sellers and what customers say about them. Reason being is while most people are reputable, there are a small few people on there who are dishonest and try to sell ones that were not brand new as though they were. However, if that ever happens, the good thing about Amazon is that any seller doing that will not only have their seller account blocked, but as amazon also control the payment process, they can refund you in full. (And the oweness is actually on the seller to prove he was legit, and not on the customer to prove it was fake.) Another good insurance measure is to video yourself opening the iPhone when it arrives, and then nobody can ever blame you if someone happens to be dishonest, because it will be impossible for anyone to dispute. Fortunately this is not something you even have to do, but I'm always overparanoid about the "what if" scenarios, that I just like to have that certainty.
Hope this helps.