What is a safe and efficient diy or commercial solution to convert 120VAC to 120VDC?
Actually, if you rectify (X) volts AC into a capacitor, you'll get (X * sqrt(2)) volts DC.  That's because AC mains are usually a sinewave specified in RMS, and the rectifier takes the peak.  If you delete the cap, then the RMS output should be closer to the RMS input, but that only plays nice with approximately resistive loads, unlike your LED's.  Probably the most practical solution, given the research that you've done already, is to use a ~35V DC supply and run your LED's in parallel.



If you insist on the series string, you might try a bridge rectifier into a series inductor and then a parallel capacitor.  This would give you better filtering than the cap alone, without adding a huge amount of resistive losses.  (though you'll still have some because the inductor also has some resistance)