That's what I did. I don't know if we can know whether they're from the same batch. Most of the sellers that are selling X5355s are actually selling batches of them, and not just singles. so, just get two from the same seller and you'll be all set. Mine are used, and they're actually engineering samples of the QVQF variety. all benchmarking software I've run sees them only as X5355, so I wouldn't worry about batches or anything like that.
but, yeah, it's as easy as searching "X5355" and sifting through the results. There don't seem to be any used ones up for sale right now, and you get a steep discount from used processors. and being that they're server processors and are built to hold up to anything/everything, i think going with used processors is the way to go. I mean, how often have you heard of a processor dying, especially a server processor?