Most caravans over the last 10 to 15 years have had awning rails at approx 225 to 240cm so most awnings are made to suit. I expect your caravan is fairly old so the only place you are likely to find a suitable awning is on eBay or somewhere similar.
The other possibility is to use a driveaway awning and modify it to fit as well as possible.
It might help if you filled in your outfit and location details so we can offer relevant advice.
I have a Gobur folding caravan and the awning rail is only about 6-7 feet high and I got an awning and porch awning from Gobur caravans, May be worth phoning them and asking the question, I kno they had quite a few secondhand ones 01263 860031
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