You may try contacting
Mark Hama Ltd.
2675 Earl Dr.
Marietta, GA 30062
markhama@comcast.net
He repairs Yashica's...but not sure if he sells parts for cameras that he hasn't repaired in-house.
On a quick advanced search of *bay, found a couple of possibilities.
Auction #s: ( 171103146083 ) ( 281131180197 )
Many of the repair parts I have purchased over the years came from *bay auctions.
Mostly, from camera repair techs going out of business. It takes a little patience...and time.
Maybe, someone with a Yashica 35 will give the measurements/dimensions of the battery
cap, then you could find a cap from another, more common camera that will fit.
Possibly, Mr. Hama, has some suggestions along these lines.
Marc