Sorry to hear that you've lost one of the screws for your transducer cover. I know how frustrating it can be when you're missing a crucial piece of equipment. I'm not sure of the exact dimensions of the screws you need, but have you considered using angle brackets to secure the cover in place? They're a alternative to screws and can be easily found at hardware stores or online. Also, if you're looking for a reliable online hardware store to browse for replacement parts, I recommend checking out
scrooz.com.au. They have a variety of screws and other hardware items.