The OnePlus 6 is already cropping up across Europe. Its available on OnePlus.com, of course, but if you dont want to use the official site for some reason, you can go through local retailers too.
In the Netherlands, belsimpel.nl has all versions starting with the 64 GB model for 520. Theres even the limited edition Silk White model, though that will ship later (June 5).
In Germany, theres proshop.de. Only the Mirror and Midnight Black models are available, not the White one. And when we say available we mean that you can pre-order them, with shipping starting on May 22.
In the UK, O2 will sell you a 128 GB model on contract for 52 a month (and 10 up front). The 64 GB model is 50 a month either thats a mistake or its totally not worth it.