Look for suppliers in your country of sale that accept dropshipping.

Look at the brands your competitors sell and reach out to them directly.

You don't need to sell all the brands in a niche, but you will want a really great collection of solid brands.

You could also start by finding smaller local manufacturers and asking if they will dropship custom products for you. Most will say no, but you really only need 1 yes for this model.

You might need to buy in advance, but you won't need to worry about warehousing.