Well, there are lots of mysteries surrounding BR. Add this one to the list. They made four sizes of Police Spinner, only 3 of which were actually used. There were three other vehicles made - the Alfa Romeo Spinner (the red car), the "lobster" car (yellow, with large forks in front), and a fuel tanker car.
The 1/4 scale Spinner is in Paris (though nobody I've spoken with including Mark Stetson) knows how it got there. It appears to be modified with some weird detail parts and a couple of graphics. The museum it is displayed in has turned down offers to have it restored and claims it is only on loan.
The 1/12th scale Spinner is MIA. I asked Mark about this a few weeks ago and he had no ide where it went. According to my notes, it was more like 15.5" long and the Anubis was something like 18" (right?). It's a pity this one is missing since it did the lion's share of the work in the film. It was built before the others, so it has the little mounts for the laser cannons on the wheels and roof.
The 4" ones were cast up in multiple but never used. I have a 3rd generation casting that is just a piece of crap. Profiles offered up a 4" a little while ago, but this was nothing more than a casting off of an original that was painted up. (I don't think it sold). The crew guys all made casting for themselves, so this one is "out there".
The 1" ones really look crappy up close. Again, they were cast up in multiples, so I'm sure they are out there as well.
The Alfa Romeo Spinner (the red one) was displayed at a VFX exhibit here in LA in the late 80's that I went to. So it is still around.
I haven't heard anything about the lobster spinner or the fuel truck. I can't remember if they were on display at the VFX exhibit.
The blimp wound up in private hands via auction.
The large section of the Tyrell building was given to the Museum of the Moving Image in New York by Mark Stetson some time ago.
The full Tyrell building miniature caught fire during filming and was junked.
Some of the other buildings were junked, but most survived as rental pieces and some of those have been sold off.
Sections of Hades show up from time to time.
Well, all I can say is remember last year's WorldCon. You never know where/when this stuff is going to show up.
Gene