Are you looking to buy a print, or just want to see it?
I don't know where you can buy one, but the One Man's Dream attraction at the Hollywood Studios has one on the wall. We took a picture of it last time we were there and then edited the pic and made a decent print.
It used to. Sadly, this picture was removed with the recent refurb of the exhibit, along with the caption of the famous account of the last time Marc Davis saw Walt when he came to view his CBJ sketches, and told him "Goodbye, Marc". These two items were positioned next to the final picture of Walt and Mickey together, and the three of these next to each other made for an incredibly touching and poignant representation of Walt's tragic passing. Now only the photo remains, which would only hold significance to Disney fans who knew it was Walt's last photo with Mickey.
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