Well, the inner Tripod CV is sure to fit the F40 on the Driver side, so you will at least have that much.
As for the other side, since you have an intermediate shaft, you could try to adapt any axle to fit that.
You might try taking your F40 to the yard with you, and test fit various axles. I would also take a turbo axle with you to compare that outer joint end, externa spline (the one that goes into the hub). The length of that shaft has to be the same, as well as all the diameters and lengths of the shoulders of the outer part of the Rzeppa shell (like where the ABS ring goes). The chances of these all just happening to be the same as the MR2 are pretty slim.
If you have a turbo hub, then you can test that too. Are there any yards near you with the honda and integra axles?
HOnestly, I think it might be a waste of time/money. Even if its only $50, that's $50 you could put towards axles that will for sure fit the F40, like Saab, and axles that will for sure fit the MR2 hubs, like a set of used MR2 turbo axles. I paid around $200 for mine off the board (I had to go get them though--2 hour drive, but got to see/visit/stay with friends)
The way to use the Honda axles would be to get the whole knuckle from the honda as well, but then you gotta adapt it to fit the MR2 Lower control arm, the strut, the brake lines, and somehow, the e-brake.
If you go with Saab/G6 axles, Joseph on the Fiero forums says resplining is about $100-115 per axle. If you re-spline MR2 turbo axles to fit the Saab tripod, its a done deal. Thats only two splines. I still have to figure out my G6 jackshaft--I think it might be too long. You could go cheap, and use MR2 the whole way on the right side, and jsut have the MR2 jackshaft machined/splined to fit the F40. Might be weird to have a Tripod on the left, and a Cross-groove on the right, but I don't think it will cause any vibration etc, as everything is CV. Of course, that right side cross-groove is known to be weak, so a pair of ATS or Chico joints are ($300? or $500?), and you end up with an extra.
I just need to check into axle length, which is next on my list, to make sure the turbo axles have enough length to re-spline --not sure yet if they need to be shorter or longer or no change in length.
BTW, Joseph suggested something about using Chrysler LHS axles. Did you find those in the catalog? He said they had the right spline count. Possilby, they are also long axles or maybe one side is longer than the other (no jackshaft).