Thank you so much for your detailed recommendations Skybreeze! I've never heard about the coconut oil treatment before, but it sounds good, I'll definitely try that at the weekend! I still have a jar of coconut oil I never use in the kitchen anyway, as we're not too keen on coconut products (we only like fresh coconut).
I've also just found a UK seller for Mane 'n Tail products on ebay. Seems to be a great product and ingredients-wise it suits my requirements. I'll try the "deep moisturising" line, sounds perfect for pony hair.
Yes, I've also read about fabric softener. Do you know how you use it, do you use it like conditioner or do you soak the pony's hair for a longer period in it?