I am a first lieutenant, there should be product kits right?
Product Kits work on a rotation, but they don't rotate in a specific order. They stay in the Garage for a certain period of time and then disappear until they are next put up, which generally isn't for a while. It's important to note that if a kit consists of items that you've already bought, its price won't go down. Also, if you buy such a kit, items that you already have in your garage won't appear again.
Regarding ranks' limitations, kits will be available until your rank is higher than the rank needed to unlock all the items in the kit or a kit with higher modifications of the items is available at your rank.
Customer support service by UserEcho