^if you are looking for old US (American) plate numbers, there are lots for sale in the US (mas mura) or through ebay (mas mahal). If you are looking for old Philippine plates, medyo mahirap bec. there was one time when all cars had to turn in their old plates when the three alphabets and three numerals license plate format came out.
I think sa probinsiya mas meron mahanap. Try antique shops, junk shops, etc...
hintayin mo VWCP (volkswagen club of the phils) meet every december, nagkalat old plates doon, less than 1k. usually sa fort bonifacio ang location ng meet na un.