Dittmer Mike - If you're asking what the Product Number of your BN SD40 is - you've already provided it (ie. 6-8585), and if you buy something new in future from a retailer the PN will be on the packaging it comes in. As for older 'used' items that are bought second hand and without any packaging, unless the Seller provides the PN you could either google the name of the item by type and its railroad name on the internet or here on the Forum and probably someone would be able to help you out.
As for your inquiry about "bigger radius track", if you're inquiring about O27 tubular track it's been around for years and is readily available at train shows, on the internet, at hobby shops, people on this Forum etc. etc. and originally came in different curvatures including 27", 42" and 54" to name a few.