Hi! So, I used to be a moderator for many years, but the game has changed a lot since then and I'm probably not a lot of help to you now.
I breed unicorns mainly. I sell uni rejects only if they have a rare coat colour.
I have unicorn foals ready for sale from Fjord team ᘛ Ʋαℓʞɣʀiεʂ ᘗ. You may see them in the breeding farm Unicorns > ᘛ Ʋαℓʞɣʀiεʂ ᘗ Sale.
Randomly, I clear out old collections of horses used either for competition filling or trophies. I also do this with BMis via the item exchange.
If a horse is not listed for sale then it is not for sale. Do not ask otherwise, thank you.