Find the replacement parts you need for the Barcelona Chair and footstool. Like these:
Knoll Barcelona Chairs:
First, of course, are the the Knoll brand Barcelona Chairs which uses screws (on the older models) or rivets (on the newer models) to attach the straps.
Replica Barcelona Chairs:
Next, there are the replicas from Italy and China.
Argentina Made Barcelona Chairs:
And finally, there is an Argentina brand of chair which were made in the 1960s through 1970s (more or less). These models have bolt together frames and have straps that wrap around the frame and are sewn or riveted together at each end to form a loop.