Part Availiability from Toyota

[JP4RNR]

I am one that generally likes to keep their Vehicles for a long time. I am finding on one of my other Toyota's (1989 4WD Van)that is 17 years old that many parts have been discontinued. A toyota parts guy told me that once a vehicle gets beyond 10 years old it can be difficult to get parts for a vehicle. I thought there was a federal law that mandated that parts needed to be availiable for 20 years after a vehicle is produced so that technically an 89 model woould have parts availiable until 2009. Has anyone ran into issues obtaining parts for their older Toyotas?