I think they already have one. It's a multi equip thing that allows you to have even 2 sheilds, 2 helms, 4 body armors lol. It automatically comes with the extra 2 accessory slots by just putting the script into your game. Thing is, I don't think you can equip the same accessory in all of those slots. The demo for it has a think where you have...
weapon
shield
armor
helmet
Accessory
Accessory
Accessory
Here's the thing, you can add even more slots. it's fairly easy to configure if you read over the script. You can even name those types of accessories too... like having the 1st for a neck piece, 2nd fora ring, 3rd for a cape, heck the list can go on to how many types of armor you want to have, to boots, gloves, and all that good stuff. You can also specify weapons that are cursed, that are 2-handed. It's a really neat script. There's a couple other features it has that I don't completely understand, but if all your looking for is extra slots for accessories, who says you need al the other features?
Anyways, if your interested search for "Multi-Slots!! v2.0 by DerVVulfman" If this isn't what your looking for, then good luck with your search.