I know she gets some of her clothes from Hot Topics, and there might be one or two of her shirts on the NCIS shop that you find at the top of the FanPop profile bar. I hope that helps some.
Check www.cafepress.com and type ncis in the search box. i think they might have a few things. u can try typing Abby ncis in the search box i havent tryed it and i dont no if anything will come up but its worth a shot!
I know what you mean wanting to know were she got all that cool clothes! If you type in Abby off ncis clothes in to Google it comes up with loads of cool stuff. Even a nice brace ball cap!!!!! Hope this helps ;)