Advanced Mounts

[Erevis Cale]

I seem to recall seeing somewhere that you could buy, say, a horse with more HD, but you have to pay the price which is XYZ gp x HD. Was that in 3.5 or does it exist in Pathfinder, too?

[Starglim]

You can buy a heavy horse, which has the advanced template (except that it doesn't increase the horse's Intelligence).

[Erevis Cale]

I know that, but I'd like to buy a heavy horse with 4 HD and I'm wondering if that's possible.