you need to be more specific -- i am guessing this is the Rollei LED with a battery that goes into a hole on the top? Rollei made many models of the Rollei 35 and they are all, frustratingly, different. The S and the SE, for example, are almost the exact same camera except for the type of meter, and yet one uses a 635 battery that goes inside, the other uses 4 tiny button cells that fit into a space on the top.
didn't those germans ever hear of standardization?
Anyway, the right model, or a picture, will greatly speed your search. ALSO, if you can get him to answer the phone or respond to email, Don Goldberg at DAG Camera Repair has a lot of this sort of spare parts for sale.