The straps for Mamma are currently not available for sale on the Internet. All you find are requests from buyers that need replacement straps.
Straps for Polly and happy snack are commonly available , from third party sellers or distributed by Chicco.
The harness for the Polly high chair is a 5 points harness very similar to chicco Mamma.
To test if the happy snack harness will fit you can go to a Chicco Shop, taking along the Chicco Mamma cover, and compare the holes in the cover with the Happy snack or Polly's one, then if it does fit, you can order the replacement harness at the shop, they will be happy to help.
Polly harness:
Chicco mamma:
Chicco polly:
Happy snack:
GENUINE CHICCO POLLY HIGHCHAIR REPLACEMENT HARNESS NEW
CHICCO HAPPY SNACK HIGHCHAIR REPLACEMENT HARNESS
All I can tell you is that all over the Internet there is NOT one single Chicco Mamma harness available for sale. Only the cover or the harness for different models.
If the Polly or Happy snack harness does not fit , then the only alternative is looking periodically on Ebay, or keep calling Chicco until someone decides to send somebody to look into the old replacement parts stored somewhere in a warehouse.
I hope this can help. This research wasted a lot of time, and I decided to post the same, even if the harness is not available. Hope not to get any negative rating.
Please let me know how it goes.
Regards.
G.