I'm not possitive and don't have a product code, but I've seen them and don't know why it wouldn't be common. I think most 5906's sold as civilian guns came with curved back straps, but I believe most LE trade-ins I've seen (especially true with 4006's) have had straight backstraps. I would assume S&W would put whatever style grip a department wanted on their pistols therefore both probably exist on LE guns. Not sure about commerical offerings.