Entirely not helpful, but apparently Whistler has some I saw them in Marshall Willanholy's Whistler gravity camp thread. I'm sure if you get "in" with any pro BMX or MXers they know of some.
The compoud it used to be called Real ride skatepark in pe,ris has one I spent alot of time in that thing. Whats your plan with the pit ?
Woodward West Action Sports Center in Tehachapi has a huge foam pit , go to woodwardwest.com for details and directions . Its 100 miles past L.A.