In their Zazzle shop, Disney offers a huge selection of officially licensed apparel and other gear. I previously shared how to use Zazzle's tools to customize race t-shirts.
Design Your Own Officially Licensed Disney Race Shirt
Zazzle also offers athletic-style leggings and all-over-print tank tops in costume style, making for easy and officially licensed costume choices for races.
The leggings are made of a comfortable and slightly compressing polyester-spandex blend. Note that these do not have pockets of any kind, so you'll have to carry any necessary nutrition and/or gear in a waist pack, armband, or other method.
The tank tops are also made of a poly-spandex blend.
I'm highlighting these for the upcoming Walt Disney World Marathon Weekend in January 2022, but these would be great for other races where running in costume is part of the fun.
Note that both of these garment styles are made using a cut-and-sew process, which means that the design elements on the different pieces of fabric might not line up exactly, which especially depends on the size of garment you're purchasing. This is normal and shouldn't be too noticeable while wearing.