Had the same issue. I think there's no lib available for recent versions of richedit/msftedit, but textserv.h provides a definition of the function, so what you can do without any need for an extra .lib is this:

// load the dll and get the function address
// PCreateTextServices is declared in textserv.h:
HMODULE h = LoadLibrary(L"msftedit.dll");
PCreateTextServices createTextServices = (PCreateTextServices)GetProcAddress(h, "CreateTextServices");
...

ITextServices svc*;
int hr = createTextServices(NULL, host, (IUnknown**)&svc);

...
svc->Release();
FreeLibrary(h);