Steering tight then breaks loose
 

Hello:
I own and love my 1985 Supra GT. A problem has shown up where, after the car sits for a while, the steering is locked but breaks loose and is fine after the engine is started after you turn the wheels back and forth a few times. I thought that is could be a power steering problem but now I don't. I believe that the ball joints need lube. Before starting the car after sitting awhile you can't turn the front wheels no matter how hard you reef on the wheel. There is a plug in the assembly to remove to install a grease fitting. Toyota here in Newport Oregon says they don't have one and the Napa store here can't find the right thread pitch to get it to fit. Anybody been through this? Need to lube those ball joints. Any help appreciated!
Mike 1985 Supra 287,000 miles and still running strong.