I am looking for vendors that might carry discs in the 110-130 range for my 5 year old son. Thank you.

http://marshallstreetdiscgolf.com (search ultralight)

Just wondering,
Are these legal to use in tournaments? I could have looked it up somewhere but figured someone would know and save me the time.

Yes. There is an upper weight limit for each approved mold, but no lower weight limit.