As Victor Bravo mentioned, I did have a very small run of extrusion made for me. Not thousands of pounds... 50lbs for my first test runs.
I had searched long and hard and was also told the same thing "Yes we do small runs" but when they got my drawings, they said great lets start with 10,000 lbs. I tend to be a bit secretive about this supplier since I know what I found is not typical, however if the OP wants to get more info feel free to PM me and we can discuss this further. Id prefer not to post this to the world as my product is only feasible price wise with this supplier and I don't want others using my supplier to make parts similar to mine.
I will say this, when I started my quote they said to get the short runs my part needed to fit within a 4" diameter circle as their short run stuff is done on a machine with 4" stock. They have since updated my dies to 5" as they no longer use that machine. So if your part is less than 5" tall, I would say they can do it on the cheap. If larger, you may need to beg a bit more as the larger machines are set up for production. My dies were cheap in the $250 to $500 range. Downside is when you do a short run, they pretty much gouge you on the aluminum price but for my needs it was no big deal as 50lbs makes a bunch of my products. I have since moved to runs of 100lbs to get the cost of aluminum down and a run of 100lb costs about 30% more than just 50lbs so its a no brainer. Also one caveat and this is a big one, they were reluctant to make my parts as they knew they were for use in aircraft. I had to prove to them my item was not a structural piece of an airframe. Th OP's spar is structural and I am unsure how they would feel about that. But they are a large company and I am sure they are making parts for aircraft, so it may be more of a function of added cost and testing involved.
Tiernay Metals was acquired by Transtar Metals which was acquired by Castle Metals.
Castle Metals [https://www.castlemetals.com/, 1-800-289-2785] has a phenomenal amount of extrusions 'on-shelf' in a huge variety of shapes, length, alloys that are certified and fully heat treated. I think they also have al large stock of light-weight 'roll-formed/heat treated' shapes [Ls, Zs, Cs, Hats, etc].
Actually I heard that some people have done something like that, yeah
You can consider checking this article http://3dinsider.com/3d-printing-basic-overview/ to actually see how 3d printing can be used for different purposes, including printing details for homebuilt planes.
However, caution: the two alloys/tempers cited... 6063-T5 and 6083-T6... have not US aeronautical equivalents, hence It may be really hard to find validated mechanical and physical allowables.
One of our European vendors used 6063-T6 tubing formed/welded to make some fuel systems components in an air refueling Manifold Assy... that was cracking at welds and proving to be less than reliable. It took me days to find referenced mechanical data... and nothing was written on the weld procedures and weld allowables. Finally found European data in their equivalent to MMPDS/MIL-HDBK-5.
It is interesting to note that this does appear to be intended for boat applications. Without a lot of other testing data for these particular extrusions [what we call 'point data' relating to a specific manufactured part]... I would not use these in critical aviation applications... unless You have very high margins of safety and a good inspection program.
I have to admit that the idea of airfoil shapes with the internal structure/surface sculpting like that is fascinating as heck to sketch into designs!