If you're not interested in master molds and the likes, and just want to add some custom made models to your collection, then I would suggest using
http://www.bluetablepainting.com
the guy running the buisness is called Shawn, and they're very well established in the community as a serious painting and modelling service. The company is about 10 people in total and one of them is a sculptor. Some of his stuff can be seen on their youtube channel (which is awesome
btw), most recently he custom made an entire Dark Elf army. And in general, their stuff is very high quality.
But check out their still pictures or some of their
HD photos (have to go about a month back on the YT channel for those) and if you like their style try and give Shawn a call, he's the definition of customer service and their motto is that they will make what ever you want them to make. Can only recommend them in the strongest if you want a professional, quick and reliable product (and they work fast on top of it

).
Cheers,
Gorlack