Do saddle bronc riders supply the halters or do the contractors?

It would be the contractors. The bronc riders have to supply their own saddles and girth/flank straps. If they also supplied the halters, then they would control which bucking horse they get, which isn't fair in rodeo competitions. Bronc riders select which horse they ride by pulling a name out of a hat, which is much more fair than them choosing which horse they should or even can ride.