Thank you Madame Toussleau. It seems like there should be a link on the Nationals page along with everything else, but you can click on links on the autocross main program page and find solo matters there. But of course, when I went to solo matters I still couldn't locate the link to the paddock registration system. I know I registered for a space, so at some point I had to have been given the link and I haven't erased anything I was sent, but I just couldn't find what seems to almost a secret site. I waded through pages of SCCA news and found a couple mentions of the paddock process, but no links.
Oh well, I don't demand perfection and I've realized for years that Nationals runs amazingly well for such a complicated endeavor. I'll mention something about this in the post-event feedback process.