Marko is giving you a excellent reference to the USA, good to look for item, but xpensive to buy due to transport and margin as these flats come from Europe!!
To purchase in Europe, the best "site" is
1)
https://www.ebay.de/ (EBay Germany) Then you enter as sorting came "flachfiguren" click on also the box " Beschreibung einschließen" on the top right (including the descriptions) to enlarge your search outside the title itself and you will get daily some 1,600 to 2,000 flats on sales from various editors (including Jupiter Miniatures, called there"Benew2001" and "pisanello" and several other ones.
If you set you selection to 200 items per page, and i sequence or sorting "Neu aingestellt" and save this to you favourtes, you a a powerful selection tool for flats in Europe.
2) Go similalry go to
https://www.ebay.fr/ (EBay France), enter as sorting criteria "plats d'etain" to search and also click in the "inclure la description" on top right and " trier: "nouveaux objets", and at bottom, 200 per page, do the same = daily some 900 flats are on sales.
3) Go similarly to
https://www.ebay.co.uk/ , but select as sorting criteria "zinnfiguren", click in also the "include the description" on top right, and "newly listed" and at bottom "200" per page
Sorting by newly listed a favourte, will alway give you the latest additions; if left free, you have the most searched, which don't give you freshed additions on sorting.
4) For the search on USA, I have not found a best sorting word to name the flats , "flat", metal flat", "tin flat figure, ... The best I am using in my favourites is also "zinnfiguren", this german denomination. However zinnfiguren is not limited to flat, but also round figures......
We can give you more link later to editors on this site here....
Try also "InZinn zinnfiguren aus Ratingen"
