You can't get stock replacement jets for the 3YF carb unless you live in a remote land and have connections with mythical motorcycle mechanics.
You may try to find a Yamaha dealer that has been around for multiple decades and ask them but don't tell them which bike it is going on. If they didn't sell it, they don't service it for the most part. Lie and tell them you have a 1994 XT600 so they know what type of jet you need and then tell them what sizes you need. Doubt they will have them but it's worth a try if you want stock jets.
Alternative main jets can be purchased at Jets R Us if you know what to look for. I found the correct type just by comparing pictures and descriptions on their site to the jets I pulled out of my carb. I think they are Keihin jets but they work. There's a Mikuni pilot that worked in my carb but it looked quite a bit different. VM28 I think. It's on the forum index somewhere.