By "at the fair" are you wanting to use them for a 4-H poultry project bird? If so, contact your 4-H leader or the extension office directly and ask for your county's regulation of this (the specifics vary from county to county - if you want to exhibit at the State Fair, though, you will want to also inquire about those regulations). I know our county is pretty relaxed about the breed issue - there are several 4-Hers who exhibit EEs and sex-links.
Another thing to ask about is open class - this, too, varies by locality. Some counties offer open class exhibits only to non-animal type exhibits, while others open some animal exhibits to open class entries as well -- they are judged entirely separate from the actual 4-H projects and are not shown in the 4-H show classes.