There are tons of "semi-custom" katanas out there.
paul chen is one big maker, but to the trained eye you can tell they are made in china, but don't mistake me they are a nice sword for what you pay.
just google paul chen and you will find the prodcut line,
he also creates a line of custom swords for
www.bugei.comThey are nice as well, but seem a little over-priced. IMHO.
also right now
www.swordstore.comgets good reviews, they look a little less flashy, but I know that their "Steel Iaito that cuts" gets real good quality tumbs up. Plus they have pretty traditional lines.
They also have the option to order a shinken from a japanese smith modern made, and totally authentic.
although be prepared to drop some $$$$$. (at least 10K, usually more like 14-15K w/ polish, mounting, and saya (scabbard).
If not that route there a literally tons of custom smiths out there.
Rick Barrett.
Michael Bell.
Howard Clark.
etc...
Although again be prepared do drop some serious change. (a full custom katana length sword, polished and mounted from an american smith will easily be 7K)
anything else you need to ask, ask away. I love this stuff.