I'll third Drive Screws from Fastenal. I thought I was the only one who knew this trick.
I've used aluminum pop rivets in size tiny or small, which you can get at Sears. But you need the tool to install them. However these leave a nub on the inside of the head tube that can hit the steerer, and might need to be ground down or cut off with a chisel. Unless you have a dremel with a flex extension, or an extension for a drill with a pin chuck, this can be difficult. Try to find the one's that have the smallest possible ball end, which will reduce this tendency.
I have some tiny aluminum rivets, of which I still have a stash. Get back to me if you need some. These are 'correct', and work well, but you need a dolly, anvil, or other tool to slip down the head tube, to contact the back of the rivet and cause it to mushroom when you tap the front with a hammer and punch. Several taps with a small hammer from the front alone are not usually enough to spread the rivet sufficiently to hold the badge securely. Normally, rivets are impacted many, many times using a vibrating hammer, which causes the stem to mushroom, and produce a 'blind' fastener, requiring no dolly on the back.
Drive screws by comparison, are extremely easy to install, and require no special tools. They come in different sizes, to fit whatever existing holes you have for the badge. However sometimes it is 'challenging' to get the Fastenal folks to sell you less than a box of 100 without pushback. They are generally an industrial supplier, and often don't prefer to deal with onsey-twosey for hobbyists. Just be polite and firm, and they will usually accommodate, although they may grumble. Be prepared for that, and take it in stride. YMMV.
Jacksonville, Oregon, USA