Jacek,
The webbing was also used on a lot of early british sports cars and also Land Rovers. I think Angloparts has the material available (at least the type shown in your last pic) and they have a distribution point in Warszawa;
https://www.angloparts.com/en/about/show/poland
As Bob pointed out...Ebay is also a good source....but also firms specialised in car upholstery and firms repairing shoes, tents and manufacture rucksacks.
Alex