Get some random Laptop power supply (up to 30V, but less is more efficient, the thing is buck/boost) and get some of these, for example:
http://www.meanwell.com/search/LDB-L/LDB-L-spec.pdf
Use one for 2 bars. You can use one voltage supply to power multiple ones, but go for a higher power rating, the driver also has loss.
Or look through the Meanwell product line for a constant current supply that can go directly to mains.