David,
The Black's Catalog value on the 4 chips that you need is a combined $36. I have the entire 21 chip set available for $48 (shipping included).
If you do not want to buy the whole set, I do have singles of the following years:
1979, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998.
Best Regards,
Murph