I'd propose that as a couple (I assume it's you and your husband) you participate in some gay group activities together that provide some kind of nudity, touch, or other activity that would provide some hot prospect a chance to see the two of you interacting and if there is some attraction all around maybe something could develop. I've met great guys in nude men's yoga classes, at organized gatherings of men nudists, men's massage workshop, Body Electric events, Radical Faerie Gatherings, etc. Even if that elusive spicy third guy doesn't show up the 2 of you can enjoy an event together! And just talking about the guys you meet with your husband can be a turn on prepare you for the types of conversations that go along with that kind of 3-way spiciness in a relationship.
But in our current corona virus pandemic and all the social distancing most of these types of events will be cancelled or postponed for months into the future. Look for guys here on LPSG that are in your area. I've used the LPSG site for striking up conversations and met up with a guy from a nearby city. As far as the gay dating apps go try signing up as a couple looking for a third and be discreet with your photos and personal data and don't post anything about your work life or that would invade your privacy concerns. There are many men on those sites that manage to hook up and keep things on the downlow and perhaps a guy that's trying to be discreet could be a good match as that's something in common right there. Just be prepared for a lot of tedium chatting with guys that never lead to anything. Pick a site like Adam4Adam and make a discreet profile and see what happens, stand firm in your privacy concerns and if a guy can't respect that move on. Check out your local Naked Yoga Philly for a start!