I had the same problem a while back - the adapters cost more than whole scope, and I couldn't test to see if it was any good without putting in a proper input signal. I asked here, and someone steered me to a lady that was selling all kinds of microwave cables on ebay. As I recall, I found some short jumper cables there that had 2.4 mm on one end, and SMA (or maybe 2.92 - SMA compatible) on the other, for about $15 each. It was not quite the same as having the precision barrel adapters, but good enough for my needs, at much lower cost. The cheapest barrel types I found at the time were about $100 each.
Just keep asking here - someone knew the right place to go (if still there) - or search the archives for 70820A, and maybe that thread will show up. It's rare enough that there shouldn't be much chaff to sort out. It would have been from about two or three years ago, I think.
Ed
