[Leica] WTB: lens shade for Canon 50mm f/1.2

[photo.forrest at earthlink.net (Phil)]

I'm looking for a clamp-on vented lens shade with an
inner diameter of 57mm. This is for a Canon 50mm f/1.2 LTM lens.
Hopefully USER condition since these things have risen above $300
lately.
Either the OEM shade would work or some other version. I could also use
a short, non-vented clamp on shade, so long as it doesn't interfere too
much with the image in the viewfinder.

(I would use a screw-in hood but I already have a 55mm UV/IR slim
filter which won't allow for a screw-in hood)

Aside from that, I'm open to suggestions on how to fabricate a vented
shade for this giant lens.

Thanks all!
Phil Forrest