They can definitely build you a custom set. Either way, you'd HAVE to have your local club/retailer, do the special order for you. Remember, it's always best to be fitted for your clubs. 

In case this is not entirely clear, Titleist doesn't doesn't do mail order.  Nor is there a price advantage to buying off the rack.  Most pro shops/advanced fitting centers will fit you with a monitor on an outdoor range.  At a price highly competitive with large retailers for off the rack/checking lie on the board for 5 minutes.  Based on you, the fitter will suggest the best selection of irons, and a mixed set with AP2s for long irons is common with CB or MB for the shorter irons.  The pricing is per club, not per set.

You can absolutely select a combo of clubs, but you may need the lofts bent so that you have the proper gap between clubs. As far as who you contact, I'm not completely sure. But I believe you can have those specifications sent out from your local Titleist retailer.