Matt I am not sure if this will help, and it may already be what Brian is planning I am not sure.
There are 6 race buoys we are very generously being given by Jules Hewson - we have used them in years gone by and seemed adequate for their purpose. They all come with weights so you may be able to use them on the new buoys. Just so you know.
Jules is away until the weekend, so I will check then when we can collect them.