Here’s a (slightly blurry) shot of the type of screws used with the Beclawat windscreen badge.
Sorry the pic is small but I can’t get it to post the full-size. It’s in my gallery at any rate.
I can’t seem to find a pic of an Elliott badge but just noticed that the folks at the Cobra Experience sell them. They have a number of original 289 cars upstairs so you might give Emily a call there. She could probably send you a pic or two and they may sell the mounting screws. 510-719-7199.