If you have the ticket numbers, you can just call them and ask them to send you receipts. Note that they do take a couple of weeks to arrive. I called about the receipts of eight trips at the end of November and they didn't arrive until this week.

I always forget to download the receipts when I check in online and the receipts are only available for about a month. Annoying. Some of my customers don't the booking confirmation emails and insist on the actual receipt with my expense claims.