A limited edition colour art book will be bundled together with volume 50. It will contain 64 colour pages that have been published in magazines before. The volume 50 + colour art book bundle is currently on pre-order for 924 yen. Once it has sold out, it will have sold out for good and don’t count on VIZ ever bringing it over. The pre-orders will ship out on March 25th, so if you want it, you should pre-order it before that.

You can get it from CD JAPAN or from Amazon.co.jp (using this guide).
Note that it ships from Japan, so shipping is a bit pricey. However, I think it’s worth it since it’s a limited edition of coloured awesomeness.

Note that Amazon’s release date is outdated. The volume 50 + art book bundle will be released on March 25th.