Sadly, most of the bike shops that used to carry tandems have gone over to the big chain stores. Circle Cycle in Torrance used to sell Santana, Burley and Cannondale. It's now a Performance. Same for one of the shops in Ventura, I think it was Rincon.
I never cared for Downey. They had a great selection, but when I went there the person I spoke with had an attitude. He pretty much treated me as if I knew nothing of bikes, and what I did, was wrong. Never went back. I'll have to check out Newbury Park.