The DTM cars body panels remained stock, there is no such thing as a "DTM body kit".
in '91, there was a DTM commemorative edition called the "Evo". This model had the same front and rear spoilers as the DTM car (DTM homologation rules of the time said the car had to be available to the general public with all aero add-ons, also look at contemporary BMW M3 Evo and Merceds 190 models wich also were available in full DTM trim - flared fenders, huge spoilers and all). Only a handful were produced.
These spoilers were never sold separately and today they are extremely hard to come by; prepare to shell out a lot of money if you find a set on Ebay.
Where are you located? US? then look at www.audiconnection.com
for manual transmission swap ideas. If you live in Europe, I wouldn`t bother with converting an auto car but buy a manual instead. Since you'd need a donor car anyway (there`s a lot more to change than just the transmission) this will make a lot more sense, especially considering that in Germany nice, good manual cars can be bought in the EUR 3000-4000 price range and even late ('93 or'94) six-speed models in top condition rarely do sell above EUR 5500.