I've only been a member for a couple of weeks, but this is a subject that has interested me for a few years. I have a balloon (still sealed in its box) that I would donate to this or future HAB projects. I see in the wiki that the current plans are to use a 350gr balloon, so this one may not be suitable for this particular project, but I am sure we can find something to do with it.
Information from the box:
Kaysam Worldwide Inc.
Nom. Wt. 800 Grams
Just let me know if it can be used.