I went to Home Depot and bought one last year. It's a Kidde brand and made for vehicle use. IIRC it was about $20. I think it's B-C rated and I think I bought the larger one rather than the little one.
The float needle stuck on my slanty last summer and when the fuel bowl overflowed and gas went out the vent, it dripped right on the exhaust manifold. As soon as I finished fixing the carb I drove right out to buy one.
Bad news is that I can't tell you how good it is.
Good news is that I have NOT had to use it yet.