We are limited right now by the fact that at this point in the offseason 20-24 teams actually believe like they have a shot to compete for a playoff spot or at least want to start off the season acting that way for their fanbase.
Couple that with what we will likely be offering for a center(ungauranteed contracts + a 1st rd pick) and there are really only a few realistic options on the trade market.
Denver is one of the few teams that because they have 3-4 deep at center they may be willing to deal one prior to the season while still maintaining an attempt for a playoff spot. So I do believe that Mozgov could be had due to the presence of Javale, Hickson, and their draftee Nurkic.
Beyond that you have to look to the obvious non playoff contenders(Orlando, Milwaukee, Philadelphia, Lakers, Boston, Utah) From those teams the only guys I can think of that we can match up with salary wise are Henson and Sullinger. Sullinger doesn't really work as a defensive add so scratch him. Henson we've talked about and if Milwaukee is open to it, I would definitely give up picks for him.
I don't see Gobert, Vukevic, or Noel as available. Joel Anthony could probably had but there is no way you give up a draft pick to get him.
So the options seem slim at this point: Mozgov, Henson on the trade market and the usual slim pickings in FA: Okafor, Oden, Jermaine O'Neal, Stiesma.
Of course, around January, when the realities of playoff positioning set in for many teams, more options will open up. But for the offseason if we can't add Henson, Mozgov or sign O'Neal, I'd just stay pat at center, and see how Andy, Tristan, and potentially Haywood can workout at center and then re-examine things mid season.