Aye, PlaymoDB is a wonderful site where you'll probably be able to find any part number you'd need (and also any information you might want to learn about older sets or parts). But keep in mind that not all of the parts are always in stock. Mostly older parts are unavailable, but sometimes newer parts are unavailable from the service.
Also, as bonniebeth said, I think it could be safely said that almost all of the times DS is mentioned here it is in the "spare parts" sense, as the actual DS sets are more or less readily available on the Playmobil site or from the catalogues.