Shipping on this coast usually works out to ~$300-350 for a pair of Sienna seats.
Your current swivel won't work with the Sienna base/seat combo I have. sorry...
(This is not directed at you leedhambly, more like a general statement about the status things...) I get asked about Sienna seats a lot. For several years, I sourced as many seats as I could, manufactured several different styles of mounting bases and sold seats and mounts to customers all over the US and Canada. In mid-'19, the supply of seats got to be unpredictable and middle man after middle man entered the game making seat prices go way up. I could no longer find seats at a reasonable price and, to complicate things further, the supply was very up and down. Sometimes there would be dozens available, sometimes you'd struggle to find one pair (then have to pay dearly for it if you were in a hurry). This made anticipating the inventory of mounts to produce difficult as well. Multiple skus, made in batches to keep costs down was actually quite a strain on cash flow. There were times when we couldn't keep anything in stock and times where parts would sit for weeks. When I took a good hard look at the numbers, I found that Sienna seats and mounts were not bringing in the return that I wanted for the amount of effort they were requiring. It was time to focus efforts somewhere else. Simple economics...and a little bit of Pareto's law.
Therefore, this pair of seats listed here, plus another pair that I plan to take out of my van once my new Scheel-Mann seats arrive, will be the last Sienna seats I will deal with. The "short" mounts that are already on this pair of seats pictured, the used "tall" mounts I have in my '$hit that takes up space in the shop' pile, the "tall-angled" mounts already mounted to the other pair of seats and two sets of Eseries driver/passenger fixed (non-swivel) adapters are everything left in inventory. Once it's gone, it's gone. I am moving on and someone else can carry the Sienna seat torch.