Some Tom bihn bags that may fit the M:

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I'm a fan of Tom bihn bags www.tombihn.com because they are well made here in the USA.

Some that might fit:

This is a doggie treat bag, but it looks like it may fit our camera with a wrist strap. Or at least as a lens swap bag:

http://www.tombihn.com/accessories/TB2110.html

He also has these messenger bags in small medium and large:

http://www.tombihn.com/messenger_bags/TB0201.html

http://www.tombihn.com/messenger_bags/TB0202.html

http://www.tombihn.com/messenger_bags/TB0203.html

These are designed to fit iPads and MacBooks respectively. Good if you shoot with eye fi cards:

http://www.tombihn.com/messenger_bags/TB0222.html

http://www.tombihn.com/11_macbook_air_bags/TB0221.html

http://www.tombihn.com/messenger_bags/TB0223.html

Waist bag with a lot of mount points that can hold an M.

http://www.tombihn.com/accessories/TB0412.html