Funny you should say that As I just bought 6 LED lamps for my instruments. I got them off eBay though:
http://www.ebay.co.uk/itm/120886470328All my instrument bulbs are the very small screw fitting like old fashioned hand torch bulbs, so I didn't bother much on checking ratings etc.
I only got around to trying one out yesterday for the first time. My garage wasn't very dark so I could barely see the light from the old or the new bulb on the speedo. Both lit up outside the instrument by touching the bulb-holder frame to the speedo bezel as earth.
The LED is a little brighter, but not a lot, so I am seriously thinking that I might take each instrument out, take it out of the case and spray the inside of the case with mirror chrome type spray paint. That should set the light bouncing around in there so that more creeps around the dial to illuminate the face.
So far I have only replaced the bulb in the speedo as the others are more difficult to get at behind the dash.