All molders and manufacturers I have worked for and with over the last 15 years use whatever is specified from the Machinery Handbood thread forms. There is no differentiation for plastics. Molders in general can hit the thread tolerance you want ,at least within a working range, even in plastic so there is no need to specify another standard.
S.P.I. (Society of the Plastics Industry) has a standard for bottle cap and neck threads. The Closure Manufacturers Association promotes this voluntary standard and you may be able to get a copy here http://www.cmadc.org/index2.tpl .