I agree that Bronica accessories are in general astonishingly cheap. The only real exceptions I think are long Nikkor teles. When I acquired most of my S2a kit maybe 10-12 years ago it was all pretty affordable, and part of the reason I've kept it even though I'm shooting more large format these days, is that it isn't really worth the trouble of selling it, because prices are even lower than they were then.
Trond, I'm surprised that you find the Nikkor 40mm soft. Mine isn't, and I'd venture that it's as sharp or sharper than either of the two Nikkor 50mm lenses (a late 2.8 and earlier 3.5) I've had. It could just be sample variation, or maybe it's been dropped at some point in its history, but an ultrawide is more likely to reveal focus issues with the camera than longer lenses, so it's worth rechecking the foam that holds down (or when it gets old pulls up) the focusing screen, which you've probably looked at in the past, and if that doesn't improve things, then the registration of the focusing helical, mirror alignment, and back issues like registration and film flatness.
That raises another point for the original poster. Earlier Bronicas all develop a focus problem that is easy to fix, and it is worth fixing this on any older Bronica that hasn't been serviced recently before even using the camera, though you might run a careful focus test with film to be sure before taking a screwdriver to the camera.
Remove the finder by lifting the tab on the front, and you'll see that the focusing screen is held down by a metal frame that is usually held in place with four screws. There is light sealing neoprene foam under this frame that presses down on the focusing screen, which should be matte-side down and resting on rails that hold it in registration with the focal plane, and there may be shims adjusting it. If you remove the focusing screen to clean in, which is a good idea, be careful not to lose track of any shims, which may or may not be there. The fresnel lens sits in a well under the focusing screen, and I believe it is usually face up, but if you decide to remove and clean it as well, note its position, so you can put it back the same way.
The neoprene foam deteriorates eventually and becomes sticky and pulls up on the focusing screen, instead of pushing it down, and pulls the groundglass out of registration. After cleaning the screen and the frame of old foam, you can replace it with the same type of foam that is used for light seals on camera backs, or you can cut up an old neoprene mouse pad and use the foam in the same way, attaching it with contact cement, or you can follow the recommendation of Sam Sherman, an guru on a few of the old Bronica lists, who used Moleskin (the kind that you put on blisters available in the foot care section of your local pharmacy) for this purpose, since it doesn't get gooey like neoprene. I've done this, and it works pretty well. If you remove the frame initially and find that there is already moleskin there instead of gooey neoprene, you can assume that the previous owner has already made this modification and put the frame back and test the focus with film to be sure everything is okay.