Just made one a couple months ago(in my gallery)- I don't have an airbrush either. I made the lid with a light grey 50/50 fondant gumpaste mix. I used Wilton's silver spray that I got at a craft store. made the lid with a 6" circle. I wanted the texture of the sewer grate so before i made lid, I made a "texture mat" out of some old leftover fondant and some spaghetti. I know it sounds crazy but it worked great. Mixed fondant with some tylose or just use gum paste, rolled it out - I broke some spaghetti into tiny uniform-ish pieces. Arranged them on the fondant in the pattern I wanted glueing spaghetti in with sugar glue. Let it dry really well. Then use to imprint pattern in sewer lid.
If this doesn't made sense let me know and I'll be glad to help. It wasn't difficult at all😊