I don't think there are any after market parts.
I always either shoot the first shot DA or leave it cocked after I rack the slide, if I'm shooting on the range.
I figure I need to practice the first DA shot anyway
Even if you can find one or have an extension added to yours, it may not solve your problem. A longer spur will probably come back and hit your hand or it may end up too heavy to give you enough hammer energy.