I run a SON hub dynamo and have recently upgraded my front light (the old light and the dynamo are ~10 years old). The new one is much brighter than the old and has a USB outlet for charging stuff, so I'm very happy with that (Lumotec Eyc).
What I want from a rear light is something like the "superflash" red LED lights, but any kind of blinking would be acceptable. Ideally I'd like one that has both constant and blinking LEDs but I have enough power available to run two, so I'm willing to keep my existing light.
I run my dyno lights constantly, day and night, so having an "off" switch is not necessary (and slightly undesirable), I'd be quite happy with a light that simply flashes whenever power is applied.
But with much searching I have not been able to find anything. I am specifically not interested in the "reelight" things, they will not work for me (and I recommend against them in general, they flash too slowly and too dimly). This thread on bikeradar didn't turn up anything. I suspect part of the problem is that blinking bike lights are not legal in Germany, home of all the good bike light manufacturers.
But I would love a link to one that I can buy, if anyone has one.
(edit in comments) People suggest I DIY, but this question arises from my attempts to DIY. I have built my own bike lights before, and it's hard to make something robust and reliable. Waterproof is a particular issue. Since the original question I have run a light designed for two AAA batteries off the rectified and smoothed dynamo output for a couple of months. Despite my efforts to seal around the hole where the wires went in the light failed after about 3 months of winter riding.
I'm currently running the SeeSense motion sensing battery light and liking the fact that I only have to touch it when I take it off to charge it - it goes into standby automatically when the bike isn't moving. But if I charge it, it stops flashing and has to be manually turned on once charging stops. So I can't possibly use that as a dyno powered light.