you could try www.jetsrus.com
many jets to choose from and they have shims as well. they dont claim to be geniune yamaha but ive done comparisons to yamaha geniune jets with measuring equipment and there is no difference. they have generic and oem replacement jets.
Good info to know, mr zaninni. Yamaha jets are so cheap online either way would be good.
There are several jet kits available for the TW, but some don't seem to work very well. Some carbs have been damaged following the slide drilling instructions that come with the kits. Perhaps someone who has had good success with a drilling project can post up the details? Any good hardware store can sell a flat washer to raise the needle. Washers are easy to make thinner with a hammer. It is rare to need to change the pilot jet--simply adjusting the pilot screw is generally sufficient.
For a stock engine, the #130 jet seems to be happy at sea level. If up a bit of altitude, the #128 is best. Way up on 12,000 foot passes, the stock 125 or 126 will be good. If your temperatures are really hot and you do a lot of sustained high speeds or super tight, steep, sandy, and/or muddy trails where speeds are low and throttle high, you might want to go one size bigger to keep engine temps down. You'll loose a bit of top end power, but not run the risk of holing a piston or burning a valve.
Generally you'll have a range of 2 or 3 main jets that tune well without obvious rideability problems. Run the leaner jet for maximum power and economy, the richer jet for maximum engine life. It's a compromise.