You can just use a showroom from the workshop. If the default one doesn't work, you can just verify local data, and it should re-download it.
Yeah this caught me out too. I was using the Silverstone showroom, but that got removed when it was removed from Steam. As Coutie stated, there is a couple defaults and some in the Workshop
ModDev Showrooms Silverstone_Showroom https://www.mediafire.com/file/ld97aqtumhxdi1x/Silverstone_Showroom.mas/file ExhibitionHangar_Showroom https://www.mediafire.com/file/x3vm1u9acf9j3ko/Exhibition_Hangar.mas/file