Many walkathons are organized to raise money for a medical cause. Larger research institutions usually set up and promote these fundraisers.
However, if you want to set up a smaller-scale community fundraising walk for your particular medical expense, you definitely can!
Get in touch with friends and family members who have supported you in the past and ask if they would be willing to participate. You can also market the event to the larger community.
Charge an admission fee and sell merchandise such as t-shirts, water bottles, and hats along the walkathon route.