If you’ve ever found the perfect pair of shoes — only to discover one doesn’t quite fit, you’re not alone. While shoppers expect shoes to be sold by the pair, not everyone needs two of them, or at least not two shoes of the same size.

Take Lisa Sommerhuber.

“I have unevenly sized feet. I just always found myself trying on the size four and the size five, and I was like, ‘Wow, on the left, the [size] four fits, and the right, the five fits,’” she says.

That’s meant buying two pairs of shoes in two different sizes. But Sommerhuber says she didn’t want to buy two pairs of shoes every time, so she founded Shoewap, an online community for people with differently sized feet. She got the idea when she was moving and giving away things to her friends. Among her stuff was a mismatched pair of shoes.

“I had bought two pairs. I had bought them in a size four and a size five. And I had one mismatch pair left over and like, ‘Obviously this is not going to fit anyone.’ And it fit one of my friends,” she says. “Among my closest friends there’s a girl who has the opposite shoe sizes to mine. And I realized I wasn’t alone.”

Sommerhuber did quick Google search and found out 10 percent of the population has feet with a full shoe size difference or more. Alec Bobroff learned that not long after buying the Healthy Feet Store in Walpole almost four years ago.

“It’s very common to have different sized feet,” he says. The store’s blog elaborates on that, stating that about 60 percent of the population has differently sized feet. For about 80 percent of those, the bigger foot is the left.

In most cases, he says, the difference isn’t a problem.

“You can size up by half a size, but if you have to size up more than that, then it probably makes sense to have two different sized shoes,” he says.

Sommerhuber says she can sometimes live with a full size difference for flats, but never heels.

“[With heels,] gravity pulls you to the front of the shoe (leaving) a small gap at the end of the shoe. Or if you take a size smaller, then the toes get squashed. So it’s either blisters or squashed toes or buying two pairs.”

Bobroff’s store specializes in orthopedic and therapeutic footwear, not necessarily odd shoes. He does sell singles on occasion. More often, he donates display models or singles from returns to the National Odd Shoe Exchange, located outside of Phoenix, Ariz. It started in St. Louis, Mo. in 1943, spurred by the polio epidemic of the mid 20th century. It runs a warehouse for single shoes and ships them to amputees and others, on a shoestring budget, you could say.

The logistics of shipping shoes can be challenging. That’s one reason Sommerhuber — who lives in Singapore — started Shoewap.com, through which members search for and offer single shoes online and exchange among themselves.

Other specialty communities have also arisen on the web.

“I discovered a forum called the Children’s Hemiplegia and Stroke Association,” says Jordyne, a Newton mom who didn’t want to use her last name. She found the group in a search for shoes for her young son, who experienced a stroke before birth and has uneven feet.

“There's this side group called the CHASA shoe exchange program. People just post shoes that they have or shoes that they may need in different sizes,” she says.

So why don’t shoe manufacturers and retailers just solve the problem by selling single shoes? Some do. Nordstrom has a single shoe program, and so do Nike and Birkenstock. But most haven’t gotten the memo.

“I would challenge other shoe manufacturers,” says Karen Lundquist, a spokeswoman for the Amputee Coalition. “It would be great if they could participate and share, share those extras that might be discarded. There's so much we don't realize that impacts people with limb loss. it seems like such a simple thing, but only needing one shoe or wanting to find what to do with a second shoe may be a big deal in somebody’s life.”

Until then, says Bobroff, “It’s really about getting the word out for people that need it.”

Robin Washington reports on transportation — including walking, especially with proper-fitting shoes. He may be reached at robin@robinwashington.com or via Twitter @robinbirk