Some time ago I came upon this issue, there was quite a bit of discussion on it at wealth-lab.com. Back then we found that WallStreetCity would allow you to download some delisted stock data in their free historical download. They had to be delisted recently and still trading on OTCBBs. Here are some symbols I downloaded.
ACRTQ ADELQ AMIIQ BHMSQ ENRNQ FDMLQ FNVG GBLXQ MIRKQ RELH THDOQ UALAQ WCOEQ
However as it turns out it is not always necessary to create a watchlist of delisted stocks. Think of it this way, some delisted stocks trade downward in pretty steady fashion before delisting making them easy to judge. What I was really after was a list of stocks with several bad price shocks which I could test against some filters, so I created a script to make a watchlist of stocks which have exhibited a 50% one day price drop in the previous four years. Whether they went on to delisting or bankruptcy is irrelavent. I tested my filters against this list. Nowadays though I simply test filters against the entire market. Some of these stocks at any one time are lining themselves up for bankruptcy, in the 50% drop list I found it's not always the chapter 11 announcement that causes the drop, often the drop happens way before that.
Here is a list of some stocks exhibiting 50%plus one day price drops :-
AAPL ABB ACF ACO AHO ALOY AMIE ARL ARMHY ARO ARTG ASF ASGR AVAN AVN AYE AZPN BCE BEAV BRIO BVEW CAPA CCRD CCUR CGA CHPC CHRZ CKC CLST CNP CNXT COMS CRY CTEC CTXS CWST DAR DKHR DLGS DRTK DVD DYN ECSI EDS ELN ELX ENTU EP EPAY ETS FDRY FFFL FHRX FMXI GES GGAL GNLB GTIV GVHR HBIO HGR HOMS ICN ICPT IDEV ILA IMAX INAP INKP INSM INTI INTV ISIS JILL JWL KSU LEXR LGTO LJPC MAXM MCTR MDCC MED METHA MSN MSTR MSV MWY NAFC NENG NET NETE NEXM NTII NTRO NTSL NUI NVEC OMG OPWV OVTI PCCC PDII PKN PKS PLMD PLXT PMTC PMTR POL PROX PRSF PTEC PTIX PVN PVSW PWR Q QVDX RATE RETK RLRN RMBS ROK ROXI RSC RSTNE RWY SBAC SBYN SEE SEPR SGI SIRI SONS SPM SPRI SRZ SVVS SYKE T TALK TCI TERN TIWI TMR TMTA TMWD TSTN TWW UCOMA UHAEQ ULTI VRSN VRTY VTIV VWKS WFR WGBC WITS WMB WVCM XING XOSY ZOMX