To find the DLL, go to your 64-bit machine and open the registry. Find the key called HKEY_CLASSES_ROOT\CLSID\{681EF637-F129-4AE9-94BB-618937E3F6B6}\InprocServer32. This key will have the filename of the DLL as its default value.
If you solved the problem on your 64-bit machine by recompiling your project for x86, then you’ll need to look in the 32-bit portion of the registry instead of in the normal place. This is HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID\{681EF637-F129-4AE9-94BB-618937E3F6B6}\InprocServer32.
If the DLL is built for 32 bits then you can use it directly on your 32-bit machine. If it’s built for 64 bits then you’ll have to contact the vendor and get a 32-bit version from them.
When you have the DLL, register it by running c:\windows\system32\regsvr32.exe.