
If you want to reroot your ponies you can find hair in a multitude of different places. Craft stores may have doll's hair you can buy. I get mine in little packettes of braided white hair. I just do a quick redye to get it the color I want my new customs or pony to have.
Hair can also be taken from donor ponies. Those are ones with bodies that are so beat up and gross that you can't save them. Just pull the tail off or carefully harvest the mane if it's long enough. Other places you can get hair are from used from wigs (stock up on these during Halloween!), dolls and other toys, such as fairy tail birds.