Is there an alternate way to get receipts from the Mac App Store
While going off of the recommendation from @Mark to contact Apple Support I found a way to (kind of) get a receipt by following the directions on this page which shows you how to get order numbers. 

Basically, in iTunes, you click on your username/email-address and then log in. This will bring up your Account Information window where you can select the "See All" under the "Purchase History" section. This will take you to a list of transactions. 

Unfortunately, you can't print these out directly, but you can take a screen grab of the receipt (Cmd+Shift+3 or Cmd+Shift+4) and then print the resulting graphic. 

A little bit of a hack, but it gets you there.