The BenQ DW-1640 is no longer in production since about two years ago and finding a new unused BenQ DW-1640 will be a very difficult task. However visiting E B a y and looking hard you might possibly find a used BenQ DW-1640. The BenQ DW-1640 is an excellent Disc Quality Scanner and as such you might consider obtaining a used BenQ DW-1640 from E B a y and use it to perform your Disc Quality Scans of your burned DVD Media.
The Pioneer DVR-115 series drive are currently in production and finding a brand new Pioneer DVR-115 series drive will not be difficult. In see you are located in USA the Web Retailer NewEgg (http://www.newegg.com) is a reliable source for a Pioneer DVR-115D.