I have done Nats once - CCbill - CCBuddie - and recently MPA3(that one was difficult)
Its not necessarily the NATS that needs designed - just need a person that can work with NATS templates and coordinate their css and such properly within those templates and your server.
http://www.lumpyimages.com/newport - check out my work - let me know if you are interested.
To quote - we would need to discuss your projects needs.