I signed up for a few consignment pages on FB for my area. I've seen people see cribs, mattress and the bedding online. Although you may have luck with actual consignment stores in Howard County.
Greenberries will take a crib - they had one recently, but not mattresses or bedding. I personally would buy a crib used, but not bedding or mattress. But Greenberries isn't very big so they might not have the space for a crib. Maybe Once Upon a Child in Ellicott City,
Re: Where to sell crib in Howard County.
I was in Greenberries (in Columbia) a few weeks ago and was told they don't buy/sell bedding.
I have a feeling you're going to have difficulty selling the crib and mattress to a consignment store because of liability. Maybe try craigs list?