There are grate style magnets the feed flows through that you bolt right to the pipe outlet. They work very well, but the problem is most of them are really heavy and I don't think you're going to want to bolt one of them to that spout. 

You might see if you can find one of this style that doesn't cost you more than what your whole grinder did. They are replaced very regularly in human food processing factories. If you could find someone who maintains the lines their old replacements would be fine for cattle feed.