how come the only billet parts i can find for an nv4500 is the input shaft why is this

 

I dont think anyone make billet parts for the NV4500 anymore however I could be wrong.

 

cuz the input shaft brakes the most, other than that the 4500 is a very strong trans

 

Because the shops who used to make them are all out of the business of making billet internals for a NV4500.The demand was low as many just ran with what they had from the factory and a billet input shaft.When I broke mine way back in 2000 I had all the billet that was available at the time installed in mine.It was not cheap but at the time I was afraid that it may break again and I didn't want that bill twice.Now some 9 years later you look back and say it was a insane purchase and wasted money as you can not get those kind of parts due to the demand being so low the shops quit making them and/or are out of business completely.

You will be fine with just a input shaft and looking back that is money I would like to have a chance to do over again.