You don't want to use that. If you can get past the smell, linseed oil has a yellow cast to it that will continue to yellow more and more as it ages.
As far as where to get it, if you don't live in California you should be able to get it at your local lumber company. It could be applied with a brush or wiped on with a rag.
For what you are doing you would be much better off cleaning the tractor and polish the old paint with rubbing compound and wax it. If you are going to coat the tractor with anything a clear coating could be done. This would require most of the prep work you would do to paint it. You would wash it and clean it with a wax and grease remover and lightly sand it with 400 grit sandpaper.