Is there any way to upgrade a Streamlight TLR-1?

[Andy]

I have several Streamlight TLR-1 lights. When I got the original a few years back I thought it was so bright. Then came the C4 that was much brighter and finally the TLR-1s, which is slighty brighter yet. I'd like to upgrade the original, older light, but I'm not finding any drop-in LEDs. Does anyone make them? Is there something else that will fit?

Thanks, Andy