I stumbled on a site not too long ago that listed specs on all kinds of tubing and pipe, what I recall is that I couldn't find od's that matched, or were slightly under, the id of 1 1/4" IPS (NRS) and moved on. Sorry I don't recall where I found it, but it was at an online AL supplier, I'm sure google will lead you there eventually.
FWIW, there is a standards for both "pipe" and "tubing" I believe pipe sizes are fewer in number and more commonly used, therefore easier to find and cheaper. What I've seen in the boat world is that most big names make their own stuff. I don't think that boads well for you idea. They wouldn't go to the trouble of making things if they could buy off the shelf products that would work (think NRS's breakdown side rail kit; a casting, machined to fit inside their tubing).
I know sawyer blades have an AL sleeve that fits into the oar (mine are the 1 3/4" shafts) and that sleeve is machined - actually it looks sanded, maybe on a simple lathe but it's definitely been worked.
I wish you luck finding such items, just be aware you may not find what you need and may need to get more creative. Remember AL is pretty easy to work so with some basic equipment you may be able to adapt things that are "close".
"If you dont do it this year, you will be one year older when you do"