I’ve applied for jobs a few times and this has always been a problem. Now that I’ve been out of college for a while it’s even more of a problem. I don’t have anyone from college that would even remember me. I can’t use my current coworkers because I don’t want my current employer to know I’m leaving until I have a new job lined up. I don’t keep in touch with old coworkers. I don’t do anything outside of work as far as volunteering or anything. I know I’m not supposed to use friends or family. Who is even left after that? The only people I have the contact info for are friends, family, and my current boss.
Maybe you are overestimating how big of a deal letting your current boss know that you are job searching really is. I’ve used a recruiting agency multiple times that requires references from two current supervisors. It always feels awkward making that ask, but it has never been the end of the world. If you are respectful and professional about it, they should be too. You can always find a way to downplay it or spin it if you need to.
That being said, of course there are petty and belligerent bosses out there. Just take a minute and consider whether that is truly the case for you or if this would just cause the normal level of awkwardness/friction that would be expected in this situation.