Get a New One
I don't think you will be able to find anyone that would switch. In fact I have been seriously looking for a 235 is a fin keel. These are not easy to fine. There is currently one for sale in the Sacramento area but I think swapping the keel would be more trouble that it is worth. I'm sure you the double labor would probably be in the same ballpark as a new keel. Check out this site, http://home.earthlink.net/~beneteau235/ by Kelly. (It's a great site about 235's.) It has a link to a person that will make you a new keel. I am seriously thinking of going this route myself. The 235 is a great boat and I live in San Francisco and a deeper keel I believe would really improve this boat in my area.--Dan