If the studio route is a no-go, check out the local colleges and universities.  Many times you will find yourself amoung, at lest, yound adults.

Also, call the local ballet companies, they have adult classes and use the fees to pay not only the insturctor but to fund the company proper.

if all else fails and you are a privateer.  call the local dance supply stores (the moma nd pop type) aske them if they know of anyone who would give private or a small group type ballet class.  Often they know the "learn in someones home" scoop.