A lot of BMW dealers, don't stock parts for old bikes, usually have to order and wait a week or so .
RealOEM.com, is a good place to start, they ask you for the last 7 characters of the bike's VIN, but it is not as current as the BMW dealer parts, but in most cases, it's usually close .
A&S BMW has an online parts site, as does Max BMW, Bob"s BMW has an extensive parts section on their website .
There's an important cut off date in R65 production, 09/80 is when the second generation of the R65 started production, look for this when you are searching for parts, if I'm not mistaken, you have a '79 or '80 bike, that is considered the 'first generation' bikes, a lot of changes were introduced with the 09/80 production bikes, and some parts can't be swapped between the two different production series .