Why do you want a precompiled kernel other than the ones on the Slackware disks ?
I've never looked for a precompiled Slack kernel but I didn't see precompiled Slackware kernels anywhere except the ones on the official Slackware site/mirror.
If you download a precompiled kernel, be aware that you download it from a site which you can trust. Two reasons for that:
And compiling a kernel from sources yourself isn't that hard