Try Henderson Defense: http://shop.hendersondefense.biz/main.sc
They don't list the details on their website but I know for a fact they're doing conversions. I saw one of their Saiga-12 conversions that was in the shop a few months ago (June? July?) and got a chance to look it over. Flash forward to yesterday..... I ended up buying one off the shelf locally and dropping it off with them to get the work done.
IIRC, they are also doing California-specific conversions with a magazine lock installed.
