Hi Mathew,
Technically you need a tax id if you are carrying on a business, however dropshippers will usually not require a tax id, only wholesalers will. So I know it sounds messy lol, but it essentially means that if you want to be completely legal and trade as a business, then get an tax id, if you don't, then that's up to you, but you will still be able to deal with dropshippers, at least most of them.