Not LEO here but... Other than a slightly shorter barrel and an extended mag your gun is more or less identical to the Remington LE 11-87 (
http://www.remingtonle.com/shotguns/1187.htm) so IMO there is not much to do other than add the extended mag if you like and a sling.
You may be able to order the parts direclty from remington or your department's dealer or from Brownells.
If yours has the J lock safety on it I would repalce that with a regular one to eliminate any chance of failure of the J lock
You can get sling adapter plates that mount between the magazine cap and ahve a slot for the sling off to the side or down below. Or you can get a "tactical" sling with the plate and sling all togetehr at
http://www.arizonagunrunners.com/Products/Wilderness/wilderness.html
Sure fire makes an intragral light equipted forend if you want one however given that you have a carbine with you already I'm guessing that you would use that primarally for "tactical" situations.
In fact if your only concern is animal calls the gun does not need much more than maybe a stock sleev to keep some extra shells at the ready. Having the extended mag would not be a bad idea to add to overall utility if your carbine went down or you chose to hand it off to another officer.
If you shorten the barrel I would go with wilson combat sights, mine has them and they work very well.
Don't let the pump crowd or Benelli guys sour you on the 11-87, it's a great gun, and very sturdy and reliable, and gas guns are not to inherently flawed or anything -- heck the M4 the military is buying is a gas gun, only downside is you have to clean it and maintian it if that can be called a downside.