Where to purchase as a new seller

I'm sorry, but no-one here is likely to give you their suppliers, as you would then be competing against them ! You need to know what category of items you wish to sell - maybe something you are interested in, but whatever, go to reputable suppliers/distributors, who give proper full invoices. Some buy from trade fairs etc. Do not buy from high street retail shops as you will only have receipts, not proper invoices, which you do need.