The key is the tractor is not on your personal residence. I have the same issue and got some great advice from a couple of TBN members. Check with your local Farm Bureau, do a search on the web and you will find them. For my area they insure through Country Financial Services. I am currently working through an agent so I don't know what my quote is yet.
I am also checking with State Farm, a couple of members also have policies through them, with their tractors located places other than their residence.