As bizarre as this sounds, would a Wii lightbar work? Each one comes with... ten LED's in two groups of five. Seems Nintendo had the same problem and rather than overdriving the LED's just pumped up the number of LED's to compensate.
The problem with the existing wii lightbar is that the wii has to be turned on before it gets power. People have made custom lightbars with the IR leds as randy suggested, or there are plenty of wireless solutions available. Funny as it sounds, people use candles instead of the sensor bar! While I'm sure it's not accurate enough for our needs, can be a pretty cool party trick.
I had to really struggle with a response to this. Partly because the OP clarified that it's the gun not the bar so there's no point going after the IR emitters. But it had more to do with just how... silly the response is.
Sure, you can blow $300 some odd dollars buying a Wii just to power a lightbar or one could simply make a trip down to Wally World, buy a $10 "sensor" bar, hack off the plug, wire it up to a 9V or higher source like a wall wart.
In all seriousness, I was thinking that the spacing on the Wii bar might be enough for the gun to register. Since I don't have the gun, I couldn't test it out for myself.
Back to the OP's problem. Maybe the cable on the gun has a short or a break somewhere?
I've heard of local people complaining the powered hub fails or "burns" out, but they never seem to want to give me the busted hub so I can see for myself.

Seems like you've already ruled out the hub though.