I bought my water decal paper off Ebay.. comes in a range of sizes.
Officeworks melbourne sell it,, cant get it here in QLD.
I used clear acrylic lacquer mixed with all purpose thinners to seal it... worked a treat.
One problem with the ink jet print is that its not that deep in colour... i ran mine through the printer twice to get good colour.. even then i ended up painting most of it too after applying.
Youd be better off getting your scan and taking it to a print shop.. tell them to print onto clear with laminate.
Print quality will be MUCH better and decal more durable.. the print laminate is really thin.. youll hardly know its there but it will protect the artwork.

To get the artwork off, I once made a mistake of cleaning an apron with meths.. took all the artwork away, but left the base colour intact