On 17th August 2010,the 10th US Navy C-40A Clipper(in civil parlance Boeing737-7AFC) was delivered.Bu number 166694 MSN 40573 line number 3346.
Published delivery date for this airplane is February 2011,so this jet may be with a subcontractor being fitted with specialist equipment until that date.
2 more C-40A are on order,so there will be enough C-40As to equip a fourth unit.
The current C-40A units are,
VR-57 NAS North Island,California with Bu numbers 165835,165836,166693
VR-58 NAS Jacksonville,Florida with Bu numbers 165829,165832,165834
VR-59 JRB Fort Worth,Texas with Bu numbers 165830,165831,165833
As far as I am aware,the identity of the fourth C-40A unitis not known.