O'reilly Auto parts and NAPA stores have batteries for the BMW. I don't know if any are in your area. Optima does not make a specific battery for the BMW, but several people on this forum have put them in their cars. I'm sure one of them can give you a part number.
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.