I wanted to start a Rogue Trader Game using the Necrons as the villans of the game and I was wondering if there were any released supplements that held Necron Space Vessel so that I could throw in a space battle or two?

Not currently. Be aware that they were extremely powerful in Battlefleet Gothic.

HappyDaze said:

However, the Newcrons are apparently less extremely powerful, since at one point a Battle Barge (one of the smaller imperial ships if I remember correctly) takes one down.

Well than what would be the chances of substituting a specified Eldar Craft that I know for sure have extensive releases in supplements  and just look in Tome Of Fate for one of the released Heavy Necron Cannons that does somewhere between 2d10 and 4d10 damage on a hit. Keep the Eldar manueverability, armor and other specs of the space vessel.

HappyDaze said:

Aye, a battle barge contains hundreds of space marines and is covered in extremely good armour, powerful engines, tough void shields and dozens of macrocannons and powerful bombardment cannnons to the fore to saturate ground targets with pulverizing fire. They also contain lots of thunderhawk gunships which while big and cumbersome are very powerful strike craft and double as boarding craft. Oh and they often have teleportariums, and dreadnoughts and terminators and tonnes of available wargear from the chapter armoury. Yeah a battle barge is a monumentally dangerous oppponent in spacebound warfare and planetary sieges.