I *think* you can get a familiar companion mount if you're a Paladin of Freedom / Ranger / Wizard/ Arcane Hierophant, with the Devoted Tracker feat.
Paladin 5 gets you a mount; Ranger 4 gets you an animal companion; Devoted Tracker makes your mount your companion and lets the abilities stack. Wizard grants a familiar. Arcane Hierophant replaces your familiar with an familiar companion. It requires nonlawful alignment (hence Paladin of Freedom) and Trackless Step, which a level of Wildrunner will get you, and 2nd level divine and arcane spells - so 3 levels of Wizard and 8 levels of either Paladin or Ranger are indicated. Wildrunner requires Elf or Half-Elf and the Endurance feat (provided by Ranger 3, of course.)
Pal8/Rgr4/Wiz3/Wildrunner1/AH4 would have BAB +17, Fort +14, Refl +10, Will +10, would cast as a Pal 12 and Wiz 7, and have other assorted oddments, like fast movement, scroll scribing for 3 spell lists, plus this strange fixation with one very strange animal. Does anyone want to work out how its properties would stack?