Johnson's Paste Wax works just fine, no need to go further than your cleaning closet or supermarket to look for something fancier.
You'll get a lot faster and better penetration (and therefore retention) if you heat the cast iron gently first. Not hot enough to burn yourself, just hot enough you don't want to keep your hand on there indefinitely (although any heat is better than none). You might leave it in direct sunlight on a warm day, set it on top of or close to a wood stove, remove the tables and stick them in your oven on warm, direct a heat blower on them for awhile, or whatever you can come up with.
Once warm, the paste wax will melt immediately on contact. Keep the surface moist with melted wax, but not so much it drips down the sides (just makes more clean-up work). Once it's sucked up all it will, let it cool completely and wipe off the excess.
You might be surprised to see how much wax it will take. What seems like a solid surface behaves more like a certain type of sponge in this case. Part of this is that paste wax is a mix of wax and mineral spirits (paint thinner to soften wax for application). The mineral spirits is what gives paste wax its characteristic smell. The evaporation of that component is what constitutes the "drying". One consequence of this is that not everything you put on stays on.
If the surface still seems dry and scratchy to the touch after you're finished, you may be able to improve it with a second application. Reports vary on that count.