All the issues of OMNI magazine (1978–1995) found on https://archive.org/details/omni-magazine including the six Best of issues.

These are CBR (rar) files, since the PDF files were too small and the text files were so full of errors they can't be read.
Use a comic book reader to view these files, or unpack them (once again, they're RAR files) for jpegs.

All the files are separated so you can grab just the ones you want, but please consider downloading and sharing all of them.