Dear Teng,
There were grey and black Velcro straps of 22,3 and 31,0 cm, respectively. The straps do not have their own NSN number but the 2 titan endpieces, which attach the strap to the watch case have. The NSN number for the Ref 3314 is : 6645-12-197-8310. I will mail to you the email address of a German collector, who might be able to help you.
Kind regards,
AVDM.