I have no problem whatsoever pulling up TK flights with fare basis GPRO1M.

Pricing US$857.40 for JFK-IST-DEL and v.v. and includes US$280 fuel surcharge and other taxes.

I cannot tell you why you are not seeing this for your particular flights, but of course you haven't provided your dates. Are you complying with the Saturday night stay requirement? And not staying beyond the 1 month maximum permitted with this fare?