The first place to check would be Fletchair. You need a spar from either a -1B or -1C. If the corrosion on the spar is that bad, how does the rest of the airframe look? Look at the inside of the skins and for any debonding issues. If it was a late production -1B the factory did primer some of the interior, but not so much on the early ones.
There is an AA-1B sitting at my airport on that I understand has not flown in well over 10 years. I don’t know what it looks like inside, but I understand the owner is about willing to give it away. I was interested to take a closer look, but I already have my ’76 AA-1B and an AA-1 Yankee project, I am out of time and hangar space as it is….
Is your son learning to fly in a Cessna 140 or Cherokee 140? I bought a Cessna 120 just after I graduated from High School in the mid 70’s. The tailwheel experience helped with the transition to the swiveling nose wheel.

• This reply was modified 3 years ago by Richard Harrison.

Yankee Aviation may have one or two of the 2-place spars.

Whoops, Roscoe is correct. I was thinking that they made a change in the center spar material with the B model as they did with the wings spars to get the GW increase. But a check of the parts catalog shows the same center spar PN 102310-1 was used from the Yankee all the way through the AA-1C. If Yankee aviation has a serviceable one, there is your source!

Just a little story on my Cessna 120, after buying it and having a friend of mine who had some taildragger time flew the plane home. In the mid 70’s there were no taildragger endorsement requirements, and insurance only stated that a CFI sign-off was needed. I had another friend that was a CFI and owned a Stearman and had a little bit of time in C-140’s give me a checkout. He instructed me in 3 point landings and told me the C-120 could not be wheel landed due to the spring steal gear, it would just bounce you back in the air. He gave me 1.2 hours of dual, signed my logbook and said to just stick to wide runways for awhile.
Somehow I kept from damaging the plane and only once felt I came close to a ground loop. And I flew out of a field the usually had a stiff crosswind.
After about 10 hours of mostly touch and go’s, one time I came in a little to fast and planted it on the mains and all went well. I soon found the wheel landings were easier the 3 point.
That next summer I spent 2 months living out of the plane while I flew around the country SF-LA-Boston-First Flight-KOSH and home. This was with a Narco Mark 4 (Coffee Grinder) radio and a bag stuffed with sectional charts. My parents wondered if I would ever come home. I have great memories of that plane, which is still flying today in England.