Many oil filters will fit BMW motorcycles. For example:
FRAM PH6063 is the correct FRAM but hard to find
FRAM PH3614 is readily available and works
AC DELCO PF-53, NAPA 1348
Mobil-1 M1-102
BMW 11.42-1 460 843 or 845
Mahle/knecht/microstar/tecafiltre OC91 (original part)
Champion C301 (of motorcycle range)
Purflux LS188B
Tech9 n??16 (France only, made by Mahle in fact)
Hiflofiltro HF-163 (from Thailand)
Mann-Hummel MW712
Detlev Louis (Germany) 10050195
Toyota 08922-02004 or 90915-YZZB9
Perf-form BMW-1
UFI makes one too (italian)
Donit 43 10 133
For After May, '97, 1100RT
Purolator P/N11421460845
AMSOIL SMF122
Bosch 3330
WalMart ST3614
Purolator L00241
AC PF53
I can't vouch for the list; I got it
here.
Not all oil filters are created equal. Because it fits and costs less isn't necessarily a good reason to use a substitute. Also, the outside diameters of these filters may vary by as much as 1/4 inch, which means your filter tool may not work with any given substitute filter.
--John