I just bought a pop-riveter at Harbor Frieght, two days ago for $5.00 - 25% coupon.
I haven't used it on ramp flaps yet. Last time I needed mine riveted, I got it done at Pinbits in person.
I was told that pop rivets won't work correctly on ramp flaps. However I used it last night on something not related to pinball and it worked. I am not sure why it wouldn't work fine on a ramp flap.