At this point, I don't think there is a way to search for plants by zipcode. You can search for plants that grow in your zone with the advanced search. However, most vegetables are annuals, so there isn't a zone hardiness category for them.
The temperatures that you see listed next to the zone don't have anything to do with the plant, those are just the minimum temps that you'd expect to see in that zone to help provide people who might not know exactly what zone they're in with a frame of reference. So in zone 8b your typical lowest winter temperature would be 15, and in zone 3a your typical lowest temp would be -39 degrees. But a plant that's listed as being OK for zones 3-8 can handle temps down to -39 degrees.