I have several large shoe boxes of duplicate US pre-cancels sorted by state, town and type; including bureaus. If you are a collector in the US let me know what you are working on and maybe I have some you need. I can send you a scan. No rare ones here. These go for 10 cents each (about half catalog, US mint OK) and SASE if it turns out I have what you are looking for. I will also exchange lots of 25 or 50 with a SASE (self addressed stamped envelope).