If you just want to swap out the mark V fork for something that isn't straight blade you will need a 1 1/8" threadless fork.
Here's a cheap and cheerful option, sells in the UK for £30 ~$60, I'm sure you can get something similar if not identical stateside, comes in chrome too. The brand is KF, try Tange too.
Alternatively, if you have enough money to buy a mark V and a $300 custom fork, a more sensible option might be to look around for a complete bike that already has a nice fork. I personally like the KHS flite 100 and Mercier Kilo TT, there is plenty of info on these if you search.
[edit] Just re-read your post and it seems you have already bought the frame, doh