I think the best place to buy them from is flytron.com I believe they are the source of the "strobon standalone" LED lights. There was a recent manufacturing defect so if you order direct from them you can be assured you will get the most recently manufactured product. Also, they were the cheapest price I could find. They are located in the UK. It took about 7 to 10 days to arrive to the US.
STROBON Standalone - Flytron I plan to attach them to my Mavic with these:
https://www.amazon.com/VELCRO-Brand-Industrial-Strength-Profile/dp/B000F5IKRA
Also, just FYI, if visibility at night is your priority then white is the brightest and most visible from a distance followed by green, then blue, and red being the least visible.