Where can I find DNA Sequence data for colon cancer
You may try the data for "Colon Adenocarcinoma" made by the TCGA project: 
http://gdac.broadinstitute.org/runs/analyses__2015_04_02/reports/cancer/COAD/

The file with mutations called by the tumor against a matched normal, 
http://gdac.broadinstitute.org/runs/analyses__2015_04_02/reports/cancer/COAD/MutSigNozzleReport2.0/COAD-TP.final_analysis_set.maf

What you need are column 11, 12 and 13. Column 11 is the reference allele (your so-call good DNA). For each row, the alternative allele (bad DNA) is column 12 if column 12 does not equal column 11, otherwise it is column 13. -- It would be a piece of cake to make by coding :)

In case you are interested, column 16 and 17 are the tumor and normal sample IDs.