As usual, I'm a little too late.

I recently came across Todd's Costumes who have brand new "repro" bags for $39 (US) plus $15 "International Shipping Charge" outside the US. They offer to give you instructions on how to "distress" it, if it looks "too new."

I did also see that an "authentic" MK VIII bag isn't "authentic Indy" because his had a non-original leather strap. Maybe that last little "detail" you need for an "authentic whichever" costume.

John