Hello doublest -
When you are in the Shipping Tools section of the listing creation page, there is an option for USPS Priority Mail Padded Flat Rate Envelope for both domestic and international and there is an option for USPS First Class Package available at this time.
If there is a specific USPS service for the type of envelope you refer to that is not available via the listing creation page, please let us know what service that is and we can forward a request to include it on to our product management team.
- Craig