Cannot find efficient current/voltage regulator to power LEDs
Try using a PT78ST106V-ND Through hole SIP-3 Module it's a 1" x 1" three terminal integrated switching regulator (ISR) which has internal short circuit and over-temperature protection as well as good line and load regulation.

http://www.digikey.com/product-detail/en/PT78ST106V/PT78ST106V-ND/323539

Number of Outputs   1

Voltage - Input (Min)   10V

Voltage - Input (Max)   38V

Voltage - Output 1  6V

Voltage - Output 2  -

Voltage - Output 3  -

Current - Output (Max)  1.5A

Here's the PDF http://www.ti.com/lit/ds/slts059a/slts059a.pdf