Hi Michelle!
Thank you for bringing your question to the Disney Parks Moms Panel!
I'm sorry that the race sold out before you were able to get registered. You are right, though, you can still register a couple of ways.
1. Travel Provider: Travel providers have bibs available for races and can offer you packages for the entire weekend.
2. Charity Groups: Similar to the travel providers, charity groups also have bibs to buy. With these groups you also commit to raising money for their cause. It's a great way to run a race and most of the groups have very reasonable minimum goals.
You can find a list with links to each travel provider and charity group on the
Walt Disney World Marathon weekend website. Just click on the "REGISTRATION" tab and scroll down.
I hope this helps! Please let me know if you have any other questions.