The general consensus is that curtains must be tailor made, like a well-fitting blazer. However, while buying single curtain panels, it is completely possible to find a perfectly-sized one off the shelf.
And these are available in a multitude of configurations. The only caveat, is that you will have to trawl through the internet for hours to find the right one. If you aren’t limited by your budget, then go for a bespoke curtain panel by all means. These will allow you to narrow down to the tiniest detail.