Hi John B,
1) Read the manual I am sure it is mentioned somewhere there, or a picture of the remote may be there and you can find its number there on it.
2) Check with Pro Fx if you have one there, I am sure someone can give you the model no of the remote + price
3) Website, down load the manual, it will mention the remote no if you have lost the printed manual also
4) Buying an all in one remote is good, but best to have the original remote and then use it to programme the all in one that you buy.
5) Some one who has your denon unit in maybe easily be able to tell your model no.
6) Buy a duplicate remote using the model no from the "Chor Bazar", electronics market etc!!! last suggestion
Hope this helps