Well, well! I just checked my rifles and found that there ARE three bolt stop lengths BUT... not in the way described above! I looked at how far back the bolt would go, I didn't actually remove the bolt and stop. Here's what I found.
T3 270win: Obviously a long action. Bolt recedes about 1/4" (ish) behind the left side of the ejection port.
T3x 308, T3x CTR 308 and and T3x 223: All the same! Bolt stops just at the left side fo the ejection port.
So who is the mystery third length?
Well, I happen to have a T3 Scout in 223, one of the ones imported around 2010-2012 with the super heavy barrel. It has a shorter stop than the other two, the bolt stops about 1/4" in front of the left side of the ejection port.
That would explain why the spare part isn't to be found. The rifle hasn't been sold here for many years. Not sure if other limited release models (like the Tactical) use the same stop.
So the summary, as reported by my stable of Tikkas is:
Long action (270, magnum length)
Short action (308 length, used for 223 as well)
Mini action? (Used on the T3 223 Scout and maybe others as well.)
I don't have a magnum caliber Tikka, I don't actually know if that bolt stop is the same as a 270/30-06.
-Stooxie