Some brands sell their baggy bike shorts and liners separately. Gore and Endura come to mind. I tend to wear my own lycra shorts under baggy cycling shorts, hiking shorts, etc.

What don't you like about bibs? There are some really nice ones out there now with zippers that make "natural breaks" a cinch and don't require you to be a contortionist to re-fasten them. Gore and Endura both offer something like this, and there are probably others too.