Check with your local boat yard(s) to see if they can supply these parts. I did that when I purchased 2 new shafts for my Spindrift Motor Yacht in Huntington Beach, CA. They sources the parts from a local machine shop.
Unless you get wildly lucky you'll pay the same freight and duty through a dealer and have to add his middleman fees as well.
Get on the internet and begin emailing boat beakers and use parts warehouses like Sailoerman in Laudedale or the place in Kemath Texas. It could take you a lot of time and effort to find this part at an affordable price, so you must decide which is more important to you;
It took me about 3 months of daily searching to locate my watermaker pump this way, but I ended up getting a bigger, new one for less that half of retail..