TheAtlasTeam

Do a Google Search for 'multi channel ecommerce software' and you will get lists of inventory management software that connects to marketplaces like Amazon and Ebay.

For example: https://www.sellbrite.com/ http://www.linnworks.com/ https://www.channelgrabber.com/ - UK based

Or if you have the startup capital have custom inventory management software created to fit your business by a software development company.