Ok ok, I'm finally going to spill my guts. I'd been planning to unveil this along with the other wonders of my mame cab, but being as the cab has been done for a year and I've still not set up a site, I'll fill you guys in on my ultimate top-fire joystick.
Remember the old wico "command control" joysticks for the atari 2600, the one's with the red handle and white fire button on top? When wico claimed to be using arcade quality parts, they weren't joking. The command control joystick shafts, springs and even e-rings EXACTLY match those of the wico arcade ball top leaf switch joysticks, and are every bit as sturdy. So there it is; buy a ball-top wico command control along with a standard wico leaf switch joystick, and you've got an authentic, versatile, super heavy duty top fire joystick that was originally intended to be used to control arcade games, not a toy grabbing metal claw.
As for trigger (not top-fire) joysticks, I have two very similar to the above assault controls, except that mine use happ universals as opposed to supers; IMO makes for easier mounting and quicker switching from 4 to 8 way. The shafts are nut drivers; I just shaped and drilled the plastic handle of the nut driver to allow me to attach the tank grips. I experimented with steel brake line for a while, but had trouble attaching it to the grip.
Making the shaft was a major pain, especially given that I didn't have a dremel tool at the time; I think if you sell just the shafts you'll have enormous demand. IMO selling the entire joystick wouldn't net you many sales, but you could of course offer both. Most of the people you'd be selling to are already at least marginally do-it-yourself types, and may flinch at paying $130 for a pair of hacked joysticks. I'm sure however that you'd have steady business with selling shafts.
If not you, then Oscar should look into adding that to his product line. Costs would be ($4 nut driver + $.50 in screws + labor). Shipping would be almost nothing, and I'm sure people would be willing to pay ~$15-$20 per shaft. Pretty nice markup.
Garv