Hello Dan, If you are on Facebook, go to our Monsters of Melodica page and send me a message with your mailing address and I will send you a small piece of neoprene that will be enough for your replacement project, just pay for the shipping. The original material that was removed seam actually thiner but I did not have a way to measure the thickness so the closes I could fine was 1/64″ I do not have an answer for the (4) rivets since there was no need to replace open the melodica. You just need to put contact cement around them so the seal can be made. Also make sure you use a sharp exact to cut the neoprene, make sure you take your time in cutting the neoprene if you cut in the wrong place you will need to start over. Please take pictures and post and share with other Melodican’s here.
Thanks and I hope this helps you