From a historical perspective, https://beocentral.com/ is perhaps the best site - however, it has not been fully updated of all products for the last few years. Some products with colour variations or MK1 or Mk2 may be lacking in the newer products (Beoplay, headphones etc). However, that can be cross references with B&O's official site for anything missing. Edit: I would also add that the accessories - both Beocentral and Bang&Olufsen will be difficult to track down without a Service Engineer or a good Dealer as these were normally sold under the radar with Customers wanting more specialised and complicated "around the House AV" Setups.

If you click the "products" tab on the main site (beoworld.org), there is quite a bit of historical information on many products.