How hard is for parasites to get new and fresh human corpses? Is the usual delivery not enough?

Well, it seems that there are not so many human corpses as you would expect, seeing how so often and easily they can get sick and die or get killed, but yes, the official delivery, the one that comes from human lands, is not usually enough. The problem is that we cannot use every corpse human´s send us. Many of them are not fresh enough or carry some human illness.

What about the amount of humans that have been moving to Forenhost lately? Does it add to the supply?

Yes, luckily, it helps. Despite most of humans that come here usually tend to come back to their human land, and if they don´t die here, we cannot use their corpses. But in recent times, the amount of humans that have decided to stay and live here has increased, so maybe in the future we will have our own supply.