I put pink cap in ebay search engine.
and i got a cap that japanese related and totally what miku would wear
http://cgi.ebay.com/CH07P-Cute-Hello-Kitty-Embroidered-Cap-Pink_W0QQitemZ170333911996QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item27 a8b13bbc&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240 %3A1318|301%3A1|293%3A1|294%3A50
!BSrJGkg!Wk~$(KGrHgoH-CEEjlLl0us,BKEZdH3n8Q~~_12.JPG
well, it fits the criteria.