Youd be better off using a flat scanner like the HP 4670... scanning the whole side, stitching together and then use Photoshop to address any blemishes etc... itll be hi res. Its still a lot of work though if you only want to print off one decal.
The decal can then be printed off by any sign place etc.. make sure you get it laminated though.. makes application MUCH easier and also acts as UV and scratch protector... the laminate comes in gloss, matt etc.
 Most decals available are not laminated.. and in all honesty, for the price charged, they should be