The Traxxas part number is 5270R EZ-Start System
it list for $50 bucks. Here's one on ebay TRAXXAS 5270R 5270 EZ START SYSTEM T-MAXX REVO NIB Item number: 220374873535
There are plenty of people selling the EZ-Start system on ebay. Just be aware that you may also need to purchase additional backplate parts for the conversion. You can also get that on ebay.
Because alot of people are doing brushless conversions on their nitro trucks, you'll see alot of people are selling complete enigine and starter system at a great prices. Your choice on what you do...I'm sure you'll get a good deal. Its very common to see these units being piece mealed on ebay.