Any information as to where I could access the one shot that used to be under this anthology? Such as whether it was taken down by a scanlator's request?

The one shot should have been called Tatoeba Konna Shimai (例えばこんな姉妹) by Itsuki Touma (東磨 樹), included in the anthology Anesama Inkou:
(https://www.amazon.co.jp/gp/product/4894219468?ie=UTF8&redirect=true)
(https://book.dmm.co.jp/detail/b216afjm00332/)