Seems like the first thing you should try is just raising the drops you have on there now. Are you riding in the drops the whole time, on the hoods or tops? I'd rather have drops for urban riding (don't know if that's where you ride), just because most mustache bars I've seen are significantly wider - seems a lot easier to me to catch your bars on a rearview mirror (or a pedestrian). Easiest thing to try would be to just flip your stem (assuming the Windsor has a threadless stem, and I'd be shocked if it didn't), that should give you at least a few cm higher position, and best thing, it's free to try.

Otherwise, yeah, any bike shop should be able to sell you a 25.4 -> 26.0 shim. For cheap. Though there shouldn't be a price difference for the same bar in 25.4 or 26.0. And if you have a co-op or decent used bike shop around, you could try buying a few cheap used bars to see what you end up liking. My two cents, anyway.