Attached you will find the PC flasher version 4.46 that works with 4600Ti (I have flashed a 4600Ti PC card using this tool so I can confirm it works) and the original Apple OEM v1105 Bios, as opposite as many ATI Cards that uses a 128k Flash ROM Apple choosen to use for the 4600Ti a regular 64k.
On this
page you will find a guide about the nvflash tool usage.
Good luck!