Honestly, and in a sincere tone, I find it hard to believe that none of the 175 movies you purchased had a DTS soundtrack. I guess that could happen because DTS is not part of the DVD standard (as it is with Blu-Ray) yet it still boggles the mind. In fact, over the past few years, I've seen more DTS than the first couple of years of DVD's. DTS has a higher bit rate and takes up more space on a DVD then Dolby Digital so some studios, when pressed for DVD space and not wanting to go to a 2 disc set, don't include it. Dolby Digital is part of the DVD standard so it has to be one of the soundtracks. Once in a while a studio did issue a "DTS only" DVD version of a movie but it was in addition to a "regular" release of the same movie on DVD with Digital Dolby.
Here's a url for the DTS web site:
Look for "browse" then use the pull down arrow to select "movie titles" and start going through the page after page of listings Just click on the page number at the bottom each page's list to get to the next one. I didn't but the first page shows up to 42 pages to go through and there's probably more after that.