Just did an Amazon search for "narrow baby gate", this came up: North States Supergate Expandable Swing Gate https://www.amazon.com/dp/B0002JETOW/ref=cm_sw_r_cp_api_nljoxbCNNCX3E

Looks like there are lots of options if you are willing to screw into the doorframe.

Edit: this one also adjusts from 26": North States Industries Supergate Classic Plastic Gate Mounts (Discontinued by Manufacturer) https://www.amazon.com/dp/B000A796WG/ref=cm_sw_r_cp_api_wpjoxbPS09XXA