You could make them yourself with 1" thick by 3" wide plate (plastic or aluminum) using a drill press and band saw. Cut into 2.5-3" long pieces, depending on the size of the sway bar. Drill the bolt holes, cut the bracket in half, place bolts in the holes to clamp it back together, then drill the bars od. If using plastic, make a top plate of .125" strip to span the bolts.
If you want to make a trick bracket for holding something else that is round but doesn't rotate, like a steering column or fuel filter, drill the parts od before cutting the bracket in half. The material removed by the band saw will be enough to clamp the filter when the bolts are tightened.
My reverse commuter trike build log: viewtopic.php?t=11384
Fitting glass and weatherstripping: viewtopic.php?f=23&t=6451
Growing various fruit trees, berry bushes, and wine grapes in zone 7b.