Goat Hide will be in high demand in Nier Replicant, popping up as an important resource in both part one and part two. Goat Hide is also one of those items that you cannot purchase in shops, so you will need to track it down in the world.
Goat Hide is farmed from goats, unsurprisingly. It is a reasonable rare drop from goats and is not guaranteed. As such, it might take a little while to get your hands on enough to fulfill your needs.
Goats can be found in two different locations. First, on the Northern Plains. The goats can be found near the mountain on the right, and near the broken bridge. The goats here tend to be outnumbered by sheep and will need to be farmed quickly as the bodies tend to disappear quite fast.
The best place to find goats is actually on the Eastern Road. This area becomes especially important in part 2, as the goats will no longer spawn on the Northern Plains during the second portion of the game.
You may need to farm the Eastern Road quite a few times to get enough Goat Hide, but that can also work in your favor as plenty of other valuable materials will also spawn along this road.