How to get Subtractive cDNA Library from reliable supplier?

Question

A subtractive cDNA library is a collection of cDNA clones which is rare and likely to be poorly expressed. Subtractive cDNA libraries are produced using a proprietary technique which relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs of similar abundance and retaining the transcripts which are differentially expressed or variable in sequence.