Hi Paulo, sorry you have had trouble finding your uphoulstry. LeBaron Bonney and SMS are the two main places most of us know about. Since they have been in business for years, I would hope LeBaron would only be out of the fabric temporarily.
The only other place that
might be able to give advice is
Enfield Auto . They make antique upholstery parts such as windlace as well as restore complete interiors for customers. They may know of another source for the correct cloth for your Fleetmaster. If anyone else has advice on alternatives, I'm sure we would love to hear from them.
All the best to you on your '47 project.