Batteryspace does make a single 26650 holder with leads. You will need to buy four and wire them in series and hold them together to make a single pack. This holder does not have any protection built in so if you want the pack to be protected, you will either have to add a protection circuit or use protected 26650 cell.
http://www.batteryspace.com/Battery-...6AWG-Wire.aspx
The other holder you listed from batteryspace for 4 18650 is fine to use with 18650. It does have it's limitation. The spacing between the ends are not wide enough to fit battery with proteccted PCB, but that should not matter since the holder has it's own PCB. I was barely able to fit non protected Panasonic NCR18650 2900 mah battery into the holder.
I see that you are planning to run a horn and other misc LED with 4 26650 or 4 18650 batteries. You posted in the OT the voltage as 14.4 volt. Are you planning to use a regulator circuit? Reason for asking is that the final charge for 4 26650 or 4 18650 is 16.8v. The nominal volt will drop to an average of 14.8v for nominal 3.7 volt cell or 14.4v for 3.6v nominal cell. However, it will remain at the higher voltage for a while before sagging down to the niminal voltage. You will stand a chance of burning things up if you don't have a regulator circuit of some sort.