+1. Measure, don't assume. 25.4, 26.0, 26.4 all look the same, but are not compatible.

Bars historically came in 38 or 40 only, at least in my lifetime. I personally don't recall having difficulty finding 40. Cinelli 66 were available in 42 but rare. These days getting dropped bars much wider is no problem. A lot of people like the Noodles. They come up to 48 cm. I haven't tried them myself.

https://www.rivbike.com/products/nitto-noodle-handlebar