Well, as I recall there was a Far Side comic several years ago with a cat that had an eyepatch sitting next to a fish bowl with a pirahna. The cat had one or two wooden legs.
I think there was a muppet cat once with a pegleg and an eyepatch as well.
The idea is not unique. Much as I like our Piratecat, I hardly think he was the first.
If one gazes back into the glory that was the 1980's, they will find that The Last Unicorn (one of my personal favorite films... see avitar) had a cat with a peg leg, eye patch, and the tounge of a old pirate... the only name the cat has in the movie is The Cat... but he was voiced by Don Messick... a man that happens to do A LOT of very excellent voice acting...
Though my researching skillz (yes, with a z) are powerful, I have yet to find a picture of the afore mentioned pirate cat on the vast internet...
However, in my searching, I did find the following pictures... beware, they may shock you.