I have used this harmonica for a couple of years when recently it stopped playing a couple notes. Assuming all I had to do was clean it, I opened it and found that it was disgusting inside. I can't remove the harp plates without not being able to put them back on since they are nails with the heads shaved down. I've seen people get screw replacements, but I cannot find a proper kit. Does anyone know of a good kit for replacement screws or the exact screw size needed?

Pictures of the mess: