Hoagies has this list here of schools:
http://www.hoagiesgifted.org/schools.htm

Some of the schools do have pre-k gifted program.

Alternately maybe a search for a NAEYC accredited pre-k program might be helpful.

A gifted 4 year old may not have that much in common with other 4 year olds (so maybe just going to a local park might be more useful and cheaper than pre-k since running around like crazy is one activity kids can do together).