I thought it might not be a huge swing - but still about 6', so decent. But you're right - further north (I'm in Friendship, ME) it is larger. So, here's another idea - although it's just a spitball type thing... With some large, SS band clamps, secure a 3' piece of 4x4 to the pole about 2' higher than the rollers woudl go at high tide. Attach this such that it is on the inside corner of the post - facing your rubrail, so to say. You can shape the backside to match the curvature with a belt sander or even just cut a narrow V-groove with circular or table saw. You don't have to be exact with this - just enough to help it "set" against the post.
To this, screw a long piece of 2x4 to it that extends vertically downward. Based on the height of the rollers above the water and compared to your rubrail height, will determine the length of the 2x4. Another 4x4 could be placed 2' below where the rollers would be at the low water mark to give another attachment point for better securement. I suspect an 10' of 2x would do it... 6' tide swing, plus 2' at each end for "just in case".
This is something that the marina should probably do for you, but it's inexpensive and I'm sure other boaters would appreciate it, too. You could even attach a vertical, vinyl rub strip to the 2x4 - although the 2x is soft enough to not cause any damage. The only thing you'll find is that you might get some wood in the phillips head screw heads from rubbing.
I'm mentioning using a 4x4 because I don't know how big those rollers are, but of course this 4x4 could be altered, if needed.
Crude drawing: