There is no comprehensive source of CRS reports, but try:
1. MNCAT; keyword "crs report" and additional appropriate keywords.
2. Google; in search box " "crs report" filetype:pdf {some keyword}". Today that retrieved about 7000 results, the vast majority of which are non-government sites.
3. Follow the suggestions in this short LLRX article: http://www.llrx.com/features/crsreports.htm#Locating.
4. When the site-wide test is set up, try out our trial of Gallery Watch, a vendor of full-text CRS reports and citations.
--Amy