Trying to buy just the brush bar hoop bits that go round the lights will be damn near impossible, believe me I tried, I had two A-bar's in the garage at one point in a desperate hope that I could source the hoop bits but never managed to get them.
In the end I ended up buying one on eBay, the A-frame plus the hoopy bits on either side. I then ended up selling the two other A-frames I had back on eBay.