Try these companies:

www.hrewheels.com
www.kinesismotorsport.com
www.fikse.com



They will definitely be able to make you wheels in those sizes, and these companies might be able to as well:
Colorado customs (not sure on link)
www.budnik.com (not sure if they do 18x13, but they do 18x12)

There are a few other manufacturers that may do 18x13, but I can't think of them currently, sorry.