So we made our own - using only materials we already had on hand.
|View from downstairs, with gate open|
First, I found a sturdy, attractive board that was tall enough to reach from floor to the top of the banister rail. It was also wide enough to cover the distance between two posts.
|Close-up, lower banister side|
|Close-up, upper board side|
To keep from damaging the banister, I cut out scraps of black fleece material for each place the board or the zip-ties would contact the banister. Holding these in place, I put a zip-tie through the hole, around the banister post and back through itself, cutting off the extra once everything was tight. Now I had a good solid surface to attach the gate to.
|Finished adapter board|
|Finished gate, open|
|Finished gate, closed|
If you don't have heavy-duty zip ties on hand - bolts from the adapter board to another small board placed on the other side of the banister would fill the same function. Even rope might work, provided it was sturdy enough, and you trust your knot-tying skills:)