Fanny No, I'm very particular; I want very specific things, Pre Raphaelite stuff or 18th century flora and fauna.
Does 18th century flora and fauna mean botanical prints or do you mean 'Still Life' paintings, those wonderful studies of bases of flowers, items on a table.
In which case auctions and ebay are your best bet. Most auctions put their catalogues online and a bit of searching should help your refine your terms to find what you want.
I recently redecorated a room and needed a pair of smallish pictures for one wall. We went to viewing day at our local auction, I walked in the door and there leaning against the wall beside the door was exactly what I wanted. I paid £30 for them, they are now in place and look absolutely right.