I have the same issue with my 23, and it did come with black plastic or nylon grommets. Most appear to have broken and fallen away. I replaced one lifeline, which came with grommets, but the outside diam is to large to fit through the hole in the stanchion. Bottom line, I am still looking for a solution.
One idea I had is to buy some of the stiff plastic tubing you can get at a big box, or maybe the clear tubing that is a bit softer, cut it into 1 inch or so pieces, slit it and slide over the wire through the stanchion. I keep forgetting to measure the OD of the wire. Of course, I don't know if tubing that has the right inner diam, and the right wall thickness to slip into the hole, is available.
If anyone knows a source of these grommets, let us know.
Peter