Bottom Line makes a side finder. I guess they are still in business. There are a lot of used ones out there for sale. I found they worked pretty good when they stayed working but then they didn't cost a whole lot.
The Bottom Line company is gone. I have one that has a 9 degree beam, that I kept to use in the manner the OP questioned. I've since sold the boat.
Clint
Far West Kentucky
Old enough to know better and way too old to care!