almost every cob series is available in 6500K including luminus, citizen, cree and others
beyond that the next step is pure blue phophor-less cobs.
cobkits.com
you could use those outright, or mix them with 6500K
Technically, per Wien's law the color temp is 6666K though thats not really relatable to white light as we perceive it
You'd need to get the peak below 450 nm to get higher color temps
there IS a relationship between a colour temperature and the peak wavelength in its spectrum. It's called Wien's law.
Wavelength (nanometers) = 3,000,000 / Col temp (Kelvin).
So at 4,500K, the peak wavelength is 666nm (red) at 6,000K the peak wavelength is 500nm (bluish green) and at 7,500K the peak wavelength is 400nm (deep blue)