You would probably need to use Watcom, OpenWatcom or the Digital Mars compiler.
Apparently, Flashtek also published a DOS extended.
You might get lucky and find a download link. I did not see one. Closest discussion was here:
http://www.digitalmars.com/d/archives/c++/dos/32-bits/139.html[
^]
If you are comfortable with writing code that makes GDI graphics calls from a WM_PAINT message handler, I'd say ditch Flashtek dependencies and write new code to replace it.