I bought two used cornies. They're pin locks, and neither of them came with Gas tubes. Will everything still work? Or do I need to buy replacements?
Are you sure they're not there? I ask because I have six pin lock kegs, and two of them have tiny gas dip tubes that are maybe a quarter of an inch long. (Just long enough to hold the O-ring.) They usually stick inside the gas post when I remove it. I can attest that these short dip tubes work just fine.
To answer your question, though, you will need dip tubes because the O-ring that creates the seal slides onto the dip tube. Without the dip tube, there's no O-ring. Without the O-ring, there's no seal.
Also, I'm not sure the poppet valve inside the post will function properly if the dip tube is missing. The gap left between the bottom of the poppet valve and the top of the nipple probably would allow the poppet valve to slide down out of position, leaving it incapable of creating a seal at the top of the post.
If you really don't have the dip tubes and just want to see what happens, you can try putting thread tape on the nipple, screwing the post on, pushing some gas in, and checking for leaks.