I've heard many times you can just call Sprint but I've never really had good luck with this. One time we got it for my friends phone after calling 4 times.
On my own EVO 4G, I used CDMA Workshop and then later there was an MSL app that came out on the market that pulled it too. Unfortunately, this MSL app does NOT seem to work on the Epic 4G Touch.
Someone told me an easier way to get it on this phone. I'm sorry I forgot who it was, it was burred in another thread somewhere on another forum. Anyhoo, it's super simple. I know this isn't anything new but people seem to still ask. Anyway here goes:
1. Download "Terminal Emulator" from the app market.
2. Open Terminal Emulator.
3. type in getprop ril.MSL (make sure the .MSL is capitalized)
4. Press enter and poof, you have your MSL code.
Again, not a new method, but people still ask. Not sure if it works on EVERY ROM, but I know it works on most of the custom ROM's.