There are some "standard" teak steps available that have non-slip grooves on one side. You may have to trim them a bit. You can also cut grooves in a flat board with a table saw.
The steps screw onto the tabs of your ladder from the bottom side. When you install them, first put the passerelle plywood in place, turn it upside down and then lay in the steps so they will support the plywood along its length after they are fastened. (The end ones, in particular, need to be spaced so the plywood can slip into its retaining structure.)
Hope this helps.
By the way, where is Moon Dog locarted.
-- Craig, SN68 Sangaris, Tropic Isle Harbor, FL