I have a swivel seat mechanism for sale.  This is the complete unit, ready to weld in and an excellent upgrade to any vanagon. 
I installed one in my syncro and I often drive around with the passenger seat reversed so I can put stuff on it like my laptop and it doesn't slide off when braking.  
I'd like to get $90 plus shipping.  I could also sell a second swivel unit if you need a pair of them.  Please email me directly if interested.
-Hans