Travel agents and AmEx aren't going to be happy about looking for reward seats for you so you should do it yourself or with the airline. If you want to use SkyTeam (AirFrance, Alitalia, Continental, Northwest, Delta, etc.) will be more likely to get you to Rome non-stop from the NYC area, but the F cabin on LH or some of the other Star Alliance partners will be a nicer trip (which is what Kagehitokiri was pointing out above).

To search for SkyTeam availability you're best off using the Continental and Delta web sites while logged in using your OnePass/SkyMiles account. This is because the carriers make more seats available for their elite members, which Centurion gets you on DL and CO. I wouldn't expect to find many seats available for this summer, but you can always try; I've seen spotty availability on AF on various dates towards the end of the summer.

To search for StarAlliance you'll need to sign up for an account with ANA, a Japanese airline in their program. Once you've signed up you can use their site to search almost all the StarAlliance carrier options.

There are a lot of other things to consider, including the taxes/fees/fuel surcharges that you'll incur (generally USA carriers will cost less than foreign carriers for rewards) but sometimes you have to go with a foreign carrier to get the seat you want (ie using AirCanada to redeem a StarAlliance flight).