Maggie here, Shopify Guru. :)
I did some hunting for you, and I actually found a few apps that do mention either pants or shorts. I am not sure if this will be enough to suit your needs, but I thought I would share anyway, just in case you hadn't seen them in your search:
Hopefully that gives you something to work with!
You can contact support 24/7 if you have any more questions!
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