You can also ask around. If you’re already connected in a Christian community, talk to friends about it - most likely, someone you know has another friend in a house church somewhere.

Finally, you can always start one. I think it’s preferable to be involved in one first, but it’s not a necessity. If you do decide to start one, or want to think about starting one, I think it’d be good to be in close contact with others who have done it in the past, read a LOT of books on the subject (I highly recommend Wolfgang Simson and Frank Viola), and find some like-minded Christians who are willing to try something different.

When my wife and I were looking around at churches after I left my church two years ago, we eventually just stumbled across a house church. But we had been mulling over the idea of starting one, and still are. I guess my point there is just to be willing to do whatever God calls you to and pursue the opportunities He lays out. But relationship is key, so pursuing it through existing relationships (whether searching for one or especially when starting one) is always a good bet.