Stamp Smarter is getting ready to release a US Plate Number Tool. It is based upon a full SQL relational database which has Scott numbers (used with permission and under contract). It does not allow anyone to download the Scott numbers or the database itself. But it is online and it is free to use. And while it contains a lot of the basic catalog information plus all known plate numbers for each stamp, it certainly does not contain any catalog values. Instead, it has links to
ebay for each stamp that users can click on and determine market value.
It is fully searchable across all fields. There is also a 'filter-in-place' feature which auto-filters in real-time when you type something in the filter boxes.
For a seek peek at this tool, you can check it out here
http://stampsmarter.com/pnt_landing.htmlNote: this is still under development. It currently includes plate number for US regular and commemorative issues 1847 thru 2002 only.