You can find all the stock roms for all the carriers here:
http://forum.ppcgeeks.com/showthread.php?t=91940
You can find the re-locker here:
http://hpcmonex.net/htc/rhodw/Rhodiu...locker_063.zip
And no you don't have to unlock your phone again. Once its unlocked it stays unlocked, but if your going to be returning this phone to sprint. Flash the stock sprint rom and then the relocker above and you will begood to go.
Don't forget to hit the thanks!