i do not believe that the AI hull is sold separately without the akas and amas.
What I believe is possible (I have done this with an AI warranty-replacement hull which was basically an Adventure hull only) is to remove all the AI componentry from an AI hull, buy a new Adventure kayak, and retrofit the AI components to that new A to make it into an AI. It isn't too hard to do as long as you have the tools, time and skill but you will be cutting holes in a brand new hull so you need to be reasonably confident in your abilities and willing to accept risks of your own making as you chop away.
HOWEVER!!!! This would leave a gaping hole in the old hull (where the AI mast base is removed from) which would render the 'donor' hull useless to all intents and purposes (unless you wanted to make an unsightly repair using PE sheet and a plastic welder).
If you want to keep the old AI hull in operation then you would need to buy a new A plus a new set of AI mastbase components to install in that new hull so that you wouldn't have to remove them from the donor hull leaving a gaping hole in the deck of that hull. You would then have an AI complete with all the akas, amas and mastbase on a new hull, and the old hull reconfigured as a A/AI half-way hybrid hull, without the akas but with the AI mastbase.
Also you would receive, with the new A hull, a drive and paddle which, if you can't make use of the donor hull, would be an expensive surplus that you may not want/need.
So it is possible, but you need to work out what you want to end up with, what you need to buy, what you will get that you may not want and do your sums!