Can't reach focus with Rokinon/Samyang 135 mm F2

What are you shooting with? 

I use that lens with either my Canon M50 or Canon RP. Have never tried it with a dedicated OSC. I do know for the two DSLRs the focus point is just a hair back from the focus stop at infinity.

Canon M50 with its M-EF adapter has a back-focus of approx 48mm.
RP with its R-EF adapter has a back-focus of approximately 44mm.

I'm sure I'm not the only one with this problem, but I can't seem to get the stars in focus given the focus travel of the prime lens.

Unless something is wrong with your copy of the lens, focus for stars in my Rokinon 135 with an Astro camera and a lens filter drawer is a 1/4" back from the focus stop.
I use a Bat mask to get mine in focus and it stays there. I do not use an EAF with mine, have not needed to once it's in focus.

Both of my copies have been able to focus at infinity from the get go, but I still did the mod to have some more space for the EAF to work. I suggest you do the mod. It's very straight forward and you can't do anything wrong as long as you follow the steps. 

You can easily test this by shooting at something in the distance, I use mountains. You'll quickly notice if the image comes into focus or not with a regular camera. As long as you can't reach true infinity, the mod is the only solution.

Just to clarify; The mod itself is a simple procedure of removing three tiny screws and a hard stop mechanism. The lens will still have a hard stop as the grooves on the helicoid aren't infinitely long, but it should now focus a bit further than infinity which allows for sharper and better focusing at distant objects like stars or even landscape. It also simplifies the AF routine with an EAF as you don't necessarily have to change too many settings (like reverse movement etc). Which is why I have decided to mod both of mine, just to squeeze any bit of left over potential from them.

The mod will not in any way damage the lens, and it is reversable at any time. Once you pull the rubber grip back on, it's like nothing ever happened externally

If your backspacing is too far off you might not be able to reach focus. It might be too short.

I just posted this picture that I took last night as you can see I can clean it up at lot with BlurXTerminator....maybe the lens was too warm when I was trying to focus early in the night...

https://www.astrobin.com/sj6t53/