Here's a link that might give you some ideas--click on 'technical information.' This is only one of the specialist bonsai potters out there. You might also check Dale Cochoy's site at wildthingsbonsai.com (although it's being rennovated at the moment.)

Bonsai pots have some special requirements to make them durable and useable for bonsai.--high firing and alot of drainage holes.

Here is a link that might be useful: Bonsai pots