Old TurboCAD design files from DOS version (.tcd) should be still supported even in latest versions of TurboCAD, so you can export them to standard DWG drawings. Sadly, we do not know about any 3rd party software that would be otherwise capable of tcd to dwg conversion.
Convert TurboCAD for DOS file to AutoCAD drawing.
We found one software available in the database for this conversion.
Microsoft Windows software - convert tcd to dwg on Windows
A family of 2D/3D CAD software products for Windows
Convert from tcd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.