You have two item-related options
The first is a mount item that will increase your speed by 1. This will translate into 5 more miles traveled each day.
Horseshoes of Speed Lvl 3 Uncommon
Mount 680 gp
Property: The mount’s speed increases by 1 square for all movement modes.
Skystrider Horseshoes Lvl 18 Uncommon
Mount 85,000 gp
Property: The mount gains a fly speed equal to its land speed.
Which won't increase your speed, but by flying you can move in a direct straight line vs. having to go around terrain like mountains, swamps, deep rivers etc.
And as as Waxeagle pointed out some other alternatives:
Light Step Feat: Elf Prereq
Will add +1 to the travel rates (hours and daily) for you and your allies.
Shadow Walk Ritual
Will multiply you and your allies travel speed by 5.