IF you would consider using a
travel agent, here is one that I used in the past that still has 10K and half available...
http://patstonetravel.com/tickets/index.php?route=product/category&path=59_61
They do now require min 2 nights hotel and min 2-day park tickets to sell the bib to you (since Disney has changed their requirements for TAs).
All just a thought, in case you had your heart set on a different race. I'm sure there are some charities out there with bibs as well, but I have never gone this route and don't have info on it. Info on charities and TAs are on rD's site:
https://www.rundisney.com/wine-and-dine-half-marathon/