At Gamecrazy or Babbages they have a ton of adaptors and stuff for older or different T.V.s for the 360..I'd try there.
I've got a 5-year-old Sony plasma monitor (PFM-42B1) that doesn't have a standard 3-prong RGB progressive scan input. Instead, it has an RGB/YUV (D-sub, 15-pin) input that I've been able to connect (via monster cables) to my DVD player and cable box. But is there a cable available to connect the Xbox 360 this way?