If you just want a dumb adapter for the samyang there are a bunch of options;
I bought a metabones Nikon-Sony E adapter for some old manual Nikon lenses just because I already had the metabones Canon adapter and liked the quality. Didn't want to order a cheap chinese version and be disappointed.
Keep in mind that there are basically three types of adapters out there:
Dumb Nikon F: For manual lenses; no aperture control (need a lens with an aperture ring or you're stuck wide open), no autofocus
Dumb Nikon G: Has an aperture ring on the adapter that allows manual aperture control with newer lenses; no automatic aperture control, no autofocus
Smart Adapter: Has aperture control and autofocus
If you want a smart adapter with electronic aperture control and autofocus you are extremely limited; I only know of two, Vello and Fotodiox. The Fotodiox had reports of being very buggy and actually damaging some cameras, and appears to now be discontinued. The Vello seems to have mixed reviews.