Latham marine is the BEST marine steering systems in the world. Go to the website for the phone numbers. It's not a full working site, but atleast you can call them to get an idea for what you need. I know they have what you need because their full page ads in PowerBoat mag always show the tie bar rods you are talking about.
In most case's (with Marine) it is cheaper to go through dealers. Here is the site for Trenton Marine in New Jersey. "Hands down" the best prices on all that I have bought from them. They sell Latham Marine products as well as other steering systems.
Note* I bought all my Gaffrig gauges from Trenton, and they were 45% cheaper than all the west coast companies out there. No kidding!!!