Last first - you have to go through an authorized dealer. Pro shop, retail sporting goods, and internet sites associated with brick and mortar sites.
The clubs all come with the split sole so that the wider base for MOI reacts with turf as if it was a narrower base for feel. The PW is 38 degrees, then there are the 43, 48 and 53 clubs that not really wedges for working around the green. I have the 6 through 43. A 20 degree 5 iron strikes some terror in my heart. I have a 23 degree 818 hybrid that is a few yards longer than the 23 degree 6 iron, then a 7W (21 degree). I still need to sort out if I have the right hybrid and if I should use a 21 TS2 hybrid instead of those 2 clubs. I do prefer to use the hybrid in difficult lies over the 6 iron. On the other end, I have always have a 48 and 54 degree Vokey wedges. I haven't used the 43 around the green or for less than a 3/4 swing (75 yard shot).
Based on flight with the 6 iron, I don't think the 5 iron will launch well enough for me to be a precise tool, as I expect it will roll too much on landing. I'd have to hit one before I buy one. Clearly, the T-400 begs a review top and bottom on how to fit these into the bag.

The lofts on the T400 irons are 'one iron difference' to the lofts on the T300 (which is approx. the same as the AP1). For example, the T400 8i has the same loft as the T300 7i at 29*.
It has been suggested that I but T400 with weakened lofts, but instead of weakening the lofts on the T400, why not just buy a set starting with the 6i [instead of the 5] ... and using the T400 8i as my seven iron .... etc etc?
Would I lose distance or something?
Thanks anyone.

Agree, I only use the number to keep them straight before pulling one from the bag. Unless I pull the 9 iron for a 6 iron. I hate it when I do that. The T-400's are easier to hit than the T-300's (before the T-400's came out, I picked up a T-300 5 iron, since I haven't carried a 5 iron for a long time). The T-400's are about an extra half club longer. The T-400 6 iron is more than 5 yards long than the T-300 5 iron. So I now have a 155 6 iron instead of a 150 5 iron.

I aspire to be you...golfing well into my 80s.