1. Welcome
2. You definitely posted this in the incorrect section so I wouldn't be surprised if the mods move this to the correct place
3. There have been a few people that have asked this same question (
DIY Idea: Installing Synchro Rev match) for example.
4. I believe your best bet would be to find a wrecked Z for these. I'm not sure I've seen any aftermarket parts so you may be limited to where you can get it from, plus it will be cheaper than trying to buy them brand new from the dealership.
5. I think cost is going to come down to how much you can/plan on doing on your own. Figure you need to drop the trans (as if you are doing a clutch change, do wiring, install the new ECU and the new gauge cluster. I'd venture to say easily 2 - 4k (depending on where you source the parts and how much you do on your own). Don't quote me on this as I am not a mechanic and don't work in a shop.