I think most of the knurled ones are still out there, just that everyone seem to be buying the large and smooth ones now.
I went in to a shop last year asking for a light weight foldable tyre, and they just laughed at me saying that noone cares about tyre-weight anymore...
I also visited a BMX-store in Flensburg, Germany last weekend and they had some new Shadow tyres for 54 euros, never seen a BMX tyre that expensive!