I guess this would depend on what you are using it for and how you plan on obtaining it.
If for duty use and depending on your department I would put in an equipment acquisition form and talk with your range master, armor, or leadership and see what they say and if it has been approved for service. This can be a long process if your department has not already approved it. If the weapon has not been approved then this would be a good opportunity for you to do the leg work. You would need to talk with department personal to determine the total cost of equipment including any maintenance and training cost. After the budget has been determined then you would need to contact distributors/suppliers and get quotes/bids from them, if your department does not already have a supplier they work directly with. You may have to send an RFP (Request for Proposal) outlining exactly what you are looking for. This form is usually copy paste and can be sent to all suppliers. Again, this is all depending on your specific department. After receiving quotes then talk with department personal, usually finance department as well leadership to see if it is something your department is willing to do. Sometimes, again, depending on your department, your local city council may have a say in this too. POST Commission may have a say in this as well, but standards and procedures have changed so much over the years they have included the Benelli as a standard practice, so this may not be an issue.
If you do not want to go this route then you would need to do it the same as the rest of us and build it out yourself. That is an expensive process that you will for sure be paying for. If you really want the 14" barrel even though you are LE my understanding is that you would still need to Form 1 it if not used for duty. As far as I know, and I may be wrong, what you are looking for does not exist in that configuration outside of department/agency request.
So basically, long story short, either one, have your department supply it for you or, two, supply it for yourself. I would personally try the first and see where you get with that. If your department has not approved it or willing to get it then you will need to source it yourself. Hope this helps. If you need any more help or questions please do not hesitate to ask.