You certainly can't buy them new so you'll have to fine a decent second hand one. Every now and again someone will break one on eBay so perhaps that's your best bet. You can try sticking an add in the "wanted" section and see what comes up. Aircooled rear seats are a lot different as the BIS ones fold flat and so have a different frame and the base squab is a slightly different shape too so you'll need both parts from a BIS
