Speaker adaptors/spacers sirion s


Just bought a 2008 Sirion 1.0 S, and i love it. I would like to fit speakers in the rear door cavities, and have bought a pair of 16cm speakers. Having removed the door trim it seems clear that I will require some spacers, so as not to fit the speakers directly on the metal.
I've googled, and the only ones which are sold as the specific fit are for 5.25" speakers.
Can anyone who has actually fitted speakers point me at the correct size/ style of spacers to fit my speakers?