The pound shop on Scarborough seafront has flying-saucer style computer mice.
Not a bad size - about 3 inches diameter - made in two tone grey/silver with a convenient hole in the underside that makes a flying stand easy to fit.
Should look ok as a 28mm 1/2 man (alien ?) scout ship or a 15mm squad vehicle.
Being a cheapskate I've kept the packaging to see if it will work as a mould for plaster cast versions too.