Cliffy sells replacement laser-cut flaps too if you get in a jam. Most people know him for protectors, but he also makes flaps...

This is exactly the same tool I use for the rivet rolling, and I made the companion tool out of a zinc 3/4" bolt (see below). The combination is perfect for setting rivets in plastic/flaps. The rivets I used are Hillman nickel-plated (not zinc) hollow tubular 1/8" diameter, and are used on pinball ramps in lengths from 1/8", 1/4", or 5/16" (or longer in a few cases). There is a thin #4 stainless washer that fits perfectly on the back (marco has these), and then using a PEENing hammer $2.99 from Harbor Freight, they assemble quite easily.

Making the Receiver using a Bolt: Take a 3/4" diameter zinc plated threaded hex bolt ($1 at Home Depot), and cut the thread part off, leaving about 2-1/2" of solid metal extending from the head. Grind the surface you just cut so that its flat and smooth and level. Make sure to grind the bolt cut edges so that they are also smooth and won't scratch any plastic if it comes in contact. Then using a drill press and 1/4" bit, drill a shallow indent about 1/8" from any one of the edges. VERY SHALLOW as it just needs to accommodate the head of the rivet. (This indent prevents the nice rounded rivet head from flattening when using the peening hammer during the installation process). I have pictures if anyone needs to see this. Just PM me.

Here you go. The Peening hammer, the HT174, and the custom back receiver I made from a HD bolt.

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Exactly why I placed the hole near the edge!!! I can get the receiver very close to the plastic ramp side, and the length of the bolt actually helps keep the plastic assembly up in the air safely. It's a simple tool, but works PERFECT!!!! Tool me 20 minutes to make. (And the rivet heads look factory set).