While we have wonderful people like Oscar and Andy creating some much needed hardware, I haven't seen anyone supplying odd sized bezels for the community.
Your basic options are Happs, Bob Roberts, Arcadeshop, etc. and I haven't seen anything there except the normal 13, 19, 25 and 27" bezels. Since these are the sizes of the arcade monitors, I wouldn't expect anything else. You might try cutting down a 25"
-- As silly as it might sound, one reason I went with an actual arcade monitor was due to the difficulty of fabricating an authentic looking bezel. My friend went with an S-video TV and pleix glass and while it looks okay, it doesn't have the right look.
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That said, I just realize that my Nanao monitor is 26" and has a 26" bezel, so there might be something out there.