Hi LadyPhoenix! I'm planning a Leon (or as I like to call him, Squeon) cosplay later in the year, so I have a couple references:
You can also use the character files in Jimminy's Journal in KH2 for a full view of Leon's costume - and you can ROTATE him too XD
One thing I have noticed, though is that in KH2 Leon's got the fur collar. The art above is a KH1 concept art, and doesn't have a fur collar on the jacket. I don't remember if he does in the KH1 game or not (it's been a while since I played it), but other than that the jacket is essentially the same. The Lion symbol is in red on the left sleeve, and there's a wing motif on the back.
Unfortunately I haven't tracked down many other references than that, but hopefully that should get you started ^^
edit: oops, found another one:
KH1 Leon Jacket Front
Looks like the jackets are different in the two games...so now it just depends on which one you're actually making ^^;