At one time, there was an annual rating list published each year in the January issue of Chess Life. They don't do that anymore, and I'm not sure if they still did it in 1998 (or, I assume what you'd really want would be such a list that would have been published in January 1999, which would have the year end ratings for 1998). If they still did, if you can find a library that has back issues of Chess Life, you could look there. Or, House of Staunton / USCF Sales has the January 1999 back issue available for $1.00.
If you can find someone who has been a USCF TD for that long, and if they're a bit of a packrat, they might still have the 1998 annual rating list, though you'd have to sort it yourself. And it might be on floppy disk... I looked on the USCF web site in the TD/Affiliate area, and they don't have rating supplements online that go back nearly that far.