I've been getting 404s, 502s and 504s quite often today, including a couple in the last 15 minutes or so. On the regular web interface, not on the miners.
While the generation of these tables isn't out of reach for a "No Such Agency" governmental organization. It is practically impossible for mining operators. Bottom line, you could potentially create a master rainbow table covering all of the possible hashes but it would be 1.06x10183 bytes in size.
The number of atoms in the observable universe is 1080[1]. No need to overestimate gov organisations.