Adam, I have information only for UCF2# models (1994-2008) rather than yours but, if they are consistent, then this diagram suggests the surround is not sold separately.
The part is described as "Speaker Assy Rear No 2" and refers to the speaker on the rear parcel shelf rather than the door speakers. The part code for this item is 86160-50100 which is almost the number in your photo. I am guessing that 86160-50010 is a manufacturing part which together with the bracket (number unknown) makes up spare part 86160-50100.
I believe Neil has a parts CD for the earlier model.