Gunsmithing Need Custom Die Made...Can Anyone Help Me

Whidden is a good bet.

Get one on order and in the meantime, use a standard seater for a 243. Not *ideal* but will work ok. In fact, if you use it carefully, it'll do a fine job.
 
+1 for CH4D. I have a set for a .408 cheytac and they are nice but you did say you are in need of a set rather quickly and getting a custom set made quickly is not going to happen unless they have a set of what you need already there. I think CH4D is a 3-6 month wait so the original set you ordered from redding may be the soonest you will be able to get them