I have not seen C-body Interior Kits anywhere, but I can advise you to use regular car screws and tuning screws. It will, of course, be a hassle to search and find something that fits. But there are similar old models, and you can borrow some screws from there. For example, at Scrooz Fasteners | Screws, Fasteners, Nuts and Bolts | Biggest Online Fastener Suppliers Australia, I found cone nuts for alloy rims and spherical and flat nuts for car interior fasteners. They have different applications but are mainly used to fasten some elements of the car. The seats of the screws are other, but you can ask them what they have in stock and on order. It will not cost you much.